We all get used to the sound of our systems. If you have 2 and one of them provides a reference it's easier to keep track of changes in the other one. Where I think it gets interesting is how your system can affect what you choose to listen to. I've had setups where I'd started to listen mostly to rock because the system suited that kind of music. The same way that certain monitors are really popular with DJ's but they sound terrible with guitar based music.
We all get used to the sound of our systems. If you have 2 and one of them provides a reference it's easier to keep track of changes in the other one. Where I think it gets interesting is how your system can affect what you choose to listen to. I've had setups where I'd started to listen mostly to rock because the system suited that kind of music. The same way that certain monitors are really popular with DJ's but they sound terrible with guitar based music.