If it's my own recipe that I'm brewing for the first time, I may just leave it since I didn't know exactly how it was going to turn out anyway. If I have a pretty good idea of what I'm shooting for or if I'm trying to replicate a trusted recipe, I'll adjust to hit my intended gravity. There are various calculators available to give you the correct amount of top-off water for dilution.
Kegged: Dusseldorf Altbier, Mild
Up next: Belgian Wheat/Rye, Kolsch