I pretty much had to have a polarity switch; My Gallo speakers are "extremely polarity sensitive," in the words of a Gallo tech. I had been switching speaker cables to change polarity, but finally gave up and bought an Aesthetix Calypso (formerly owned a CJ Prem 17LS2) with polarity switching via the remote, and haven't regretted it. Most speakers won't even reveal polarity changes, but if you have a pair that does, a polarity switch becomes kinda important.
I have a linestage that has a remotely controlled polarity switch (Levinson Ref. No. 32) and others that do not have such a switch. I like having the ability to make a switch for near instantaneous comparison, but, not having such ability is NOT a deal breaker for me.
I find that, with a lot of recordings, switching absolute polarity has mixed results, for example, the vocals may sound better one way, but the piano now sounds oddly phasey. One can be unduly distracted by trying to find the best position (this can change from track to track on a given recording). My current linestage does not offer this ability, so, I largely ignore the issue even though I know that there is a difference.
I have it on my Wyred 4 Sound Dac2 and Integrated amp. I can almost always hear a difference on my recordings and have a preference one way or the other for a given recording. I switch from the listening seat via the remote so I don't need to get up and down and the reversal is instant. Since the reversal is done in the digital domain, I don't think it affects the sound quality at all.
I have another "more pure" system without polarity reversal and I really miss having polarity reversal in that system.
In all of my years in the audio hobby I have only had a phase switch once. It is on my recently acquired Octave jubilee preamp. I have experimented several times and have concluded it makes a difference on certain material. For example, I was playing an LP that I thought sounded kind of thin and closed in Now for most of my lp's, they do not exhibit this anomaly. This one LP did and I reversed the phase on the preamp and what a difference. Generally speaking most music can be played back without thinking about phase settings. Every once in a while you come across a situation where you wish you had or just carry on. The fact that I did not use a phase switch before does not mean that I do not want it when I need it. It is like having a spice or something of that nature. You probably could live without but if you had, use it. So, a phase switch is not a deal breaker for me, but, since I have found usefulness in having one, I may be more Inclined to seek out that option in any future upgrades, which at this point I do not see happening to soon.
Viridian, I can't speak for all preamps but on our preamps the phase switch is very simple, as our preamps are internally balanced. So to do the phase reversal requires no circuitry other than the switch itself.
I have found that the switch does not have much use unless you are listening to a fairly pure recording- one that is done with a minimum of microphones (hopefully only 2 and if there is a third it is the center channel). Then the difference can be quite noticeable. I've not found the speakers to play a huge role in this.
Ralph is Ralph Karsten, the founder and principle designer of Atmasphere electronics. His designs are fully balanced, so, phase reversal is accomplished just by using a switch. Single ended electronics would require an additional "active" amplification stage, and for that reason, there is much more of an issue of whether the sonic benefits of the ability to reverse polarity is worth the inevitable degradation from having another amplification stage.