Splitting cable - degradation of signal

Would like to add a forth splitter of the incoming coaxial cable.  So far no discernible quality impact after 3 splits.  Not much demand overall.  How will adding a forth splitter to be used for modem and tv impact signal to tv and especially quality of hifi streaming.

( former cable tech )

i would not add a 4th splitter as you will lower the signal coming in and will raise the return        ( signal going out ) .          for internet a modem is happy with the forward signal at -8 to +4 and the return level you don’t want to go any higher than 52......it can go to 54-55 but that is really pushing it.       if the return level is to high, then this is where you will see pixels and streaming will have issues.         

then you have to also look if you run the line yourself, if you don’t do correctly, you could cause noise out on the plant, which in turn would cause your neighborhood to have issues and you could actually cause an outage.

there is more.....but this is just part of it.
What about adding a device to amplify signal?

hear that even connecting additional splitters will impact quality even if not in use.

so are we resigned to only having 3 TVs and one modem?

i wanted to set up another home theatre room in home.  
Thanks for you really good answer above.
you can add a amp which will increase the tv signal, but you don’t want to have the internet line amplified.      what they will put before the amp is a dc or two splitter and one leg of the dc would feed the modem and the other leg from the dc / splitter would go to amp / splitter for tv.

i don’t suggest you do the amp as you could easily cause the issues that i mentioned earlier .  your cable company can easily have the lone installed, verify levels are good and if a amp is needed, then they can put one in

if a tv outlet is connected to a splitter and the tv is not on , it is still active per say and signal is effected.....as all you have to do is turn the tv on and you have tv.        
Former cable tech - do you have home run lines to each location and the ability to add more home runs?  If you have home runs then you have the option of getting up to 8 ports with equal signal and return from a Unity Gain amplifier.  Passive splitters reduce the signal by specified amounts of loss which can be detrimental to the QoS (quality of service).  Unity Gain is like having the same incoming signal sent out to each line with no loss (passive splitter).