Gain stages on Preamp

What is the purpose of adjusting the gain stage on a Preamp? Does a Solid State amp vs a Tube amp dictate up or down on the gain stage? What are the Pros and Cons of turning it up or down?
Thanks Pete
The main benefit of adjusting gain at the pre-amp it to match the amp(input sensitivity) and speaker SPL. Too much gain and/or too much amp sensitivity and/or speaker SPL and you will raise the noise floor substantially and reduce the range of the volume attenuation control on the pre-amp, i.e. the usable level of the volume control is between 8 and 9 o'clock if the gain is too high or the amp/speaker is too efficient. You loose small gradations of volume level which is usually available when your volume control is about 12 o'clock (+/-) on many but not all attenuators.

It doesn't make any difference whether is ss or tube, but the noise floor issue is much more common with tubed units and very efficient speakers (90 DB+) With speakers over 100db it can be critical.
Volume controls are very imperfect beasts. They are at their most linear completely open, out of the circuit. The further you turn them down the less linear they become. So the purpose of adjustable gain is to be able to use the volume control over the maximum part of its travel to reduce non-linearities and channel imbalance.
good answers by Newbee & Viridian. I'll add my 2 cents:
the gain control on a preamp is really an attenuator as already indicated. The CDP or any source outputs a fairly large signal that, if unattenuated, would exceed the max input voltage level of the power amp that is required by the power amp to produce its max output power. IOW, if the source signal is unattenuated you would be listening to music at max output power which would make your ears bleed.
So, you turn the volume control to adjust how much of the source signal gets thru to the power amp.
In many vintage preamps & integrateds you could see the 6 o'clock position labeled as 'minus infinity' i.e. max attenuation i.e. none of the source signal is getting thru.
Tube vs SS: generally, you are dealing with more noise in a tube cot but not always. There are some very, very good tube preamps out there that have practically no noise at low levels of attenuation.
Given that tubes can be as good as SS (or SS can be as good as tubes - depends on which camp you prefer to be in.... ;-) ), implementation of the volume control is more important. Resistor ladder vs. transformer type - some people prefer one type vs. the other. Many feel that transformer type volume control is more transparent than resistor type altho' Placette Audio made a very transparent resistor ladder volume control, if memory serves me correctly. Volume control can also be done digitally (as was the case in many Wadia CD players) as is the case in many digital power amps today & several DACs as well. Here, as the volume is turned down the SQ degrades rather rapidly. I'm sure that many strides have been made to improve this today but I have not had the chance to hear a present-day digital volume control.
Pros & Cons to turning it up/down: turn it down & your wanted signal is not much higher than the noise floor of the electronics used to create the preamp function. This means that the power amp is outputting a low wattage signal to the speaker & you have low SPLs in your listening room. Many speakers do not fare well at all with low SPLs in that the music does not have the vibrancy that engages the listener emotionally. There voltage drive to the drivers is too low for adequate SPL.
Turning it up too much, while you are operating in the more linear region of the volume control, you boost the signal & the noise (from the electronics). While your signal-to-noise ratio is high (which is what you want), your noise is higher too. Plus, with such a high signal level running into your power amp, the power amp is operating closer to its max output level hence the distortion from the power amp will also be higher. This will have its detrimental effect on SQ.
So, there is a sweet spot for the volume control - I;ve found it to be in the 12 o'clock to 2 o'clock position (if your source allows such a thing) - where the SNR is high enough & the noise (while higher) is not high enough to degrade the SQ. I also found that each recording (CD) has its optimum volume control where it sounds the best. This, of course, depends on system-system.
Thank you all for the info. So the best way to set the gain stage on the preamp would be to set it to zero and put the volume where you like to listen then slowly turn the gain up to where the music sounds its best???This will be a new preamp matched with a large older solid state amp. The speakers are 93dbB@W Matrix 800-Esoteric CO3X preamp and a Mark Levinson 335 amp. Any suggestions at all thanks
Good question!
05-20-15: 68pete
Thank you all for the info. So the best way to set the gain stage on the preamp would be to set it to zero and put the volume where you like to listen then slowly turn the gain up to where the music sounds its best???
68pete, maybe you are making this way more complicated than it ought to be. I'm not sure what you are driving at with your question??

set the volume knob to whatever level you want to listen to music at that time - maybe you are in a mood to listen at low volumes? maybe you are in a mood to listen at higher volumes? Maybe you are listening at night when the family is asleep & you can only listen at lower volumes? And, there are many other situations that might dictate the volume setting - who knows.....
your volume setting for that listening session might not line up with the volume setting at which that music sounds its best. Does that mean you are not going to listen?? Probably not!
Just set the volume to what your needs are at that time. Playing around with this control (if you are able at that time) you'll find that best volume setting. Make a note of it (a friend put a Post-It note on the inside cover with that best volume setting) & move on...
05-19-15: Bombaywalla
good answers by Newbee & Viridian. I'll add my 2 cents:
the gain control on a preamp is really an attenuator as already indicated.

Gain control in stages are voltage dividers
same thing (synonym) Czarivey - voltage dividers, attenuators. they reduce/attenuate the voltage coming out of the preamp.
I like using dual volume. In my analogue setup I use Nakamichi RX202 tape deck to provide extra boost to phonostage. That extra boost I can vary from record to record and achieve an ideal volume settings per listening I desire.
yeah, I see what you are saying - the flexibility is good but you have one more distortion-creating device in your signal chain which is not good IMO but if it works for you-great! :-) I feel it's better to have minimum electronics in one's signal path with each device correctly designed for the job. This way one does not need to band-aid.....
It trades off. The right volume takes care of distortions.