What I did, because I'm using the tdc mod, is I made a few markings on the screw I'm using and a marking on the stock. I line up the first one for my .25s, the second for my .3s, etc. I use different weights because if I am just shooting targets, I might use lighter or heavier bbs so I know the characteristics of all of them. That way if I am forced for whatever reason to use a different bb than normal, I will have no problem adjusting. I recently got the r-hop though so it's going to be fun tuning that.
For the most part, once you find an fps you like, or a spring you like, you aren't going to change. Unless of course you use a more powerful spring for target practice, which some of my friends do. But really, if you do that, it's not really practice, is it?