Some bikes will benefit from additional steering lock in the tight woods. I ground down the stop on my old KDX250 quite a bit - that bike needed it. I removed material from both sides of the tab on the steering head and repainted it afterwards.
The thing to watch out for is the fork tubes hitting the gas tank at full lock. If you grind down the stop too far, it would be possible for the forks to knock the tank loose in a crash. Other than that, I can't think of any adverse effects.