Mine was not severe, so it did not hinder me at all.  The noise I heard was a 40db loud test tone @ 5k (at a narrow range).  I started doing my initial mixing and mastering at around 85dbs, so the tinnitus tone was pretty much masked (drowned out).  Its kind of like when someone records mic hiss.  You can hear it when the music stops, but when the guitars are playing you can't hear it at all because the hiss is being masked.

Singer Phil Collins retired because of his tinnitus.  Bono also has very severe tinnitus that greatly affects his everyday life.  If your tinnitus is very severe like those two, I'm sure your sound engineering skills would be greatly affected.