Using all these various systems from simple low cost speakers to state-of-the-art stereo systems will let you make adjustments to your master recordings so you get "good" sound from all peoples systems. A typical issue/problem is to monitor your recording only with a state-of-the-art stereo system is you tend to crank up the bass because your system can handle it AND deliver it! But, when you listen through a small system it overloads small speaker systems.
The opposite can also be true! If you monitor your masters on a small, bass deficient speakers, then you will tend to pump up the bass, and when you listen to your mix on a bigger, full bass system, the bass will be way too heavy.
Another issue is putting a lot of stereo panning effects into your tracks, which may sound great when listening through speakers, but will sound terrible when listening with headphones, which is much more common with all the millions of Apple iPods out there :) - so give your final mix a good listen with headphones too.
Enjoy! Create! Share!
(posted by jaggerdiggydog)