Hmm...
How nimble are we talking?

I'm guessing that we're not talking about dodging missiles and bullets. I'm not sure how much unpredictability factors into a battlefield where guided missiles and computer aided targeting are commonplace.

I can see that it could come in handy in edge cases, but mechs also suffer from terrible armor placement and a taller profile. You're sacrificing a lot of durability for a little bit of maneuverability.

That said, the fact that mechs can sidestep and pivot in place (presumably faster than a Scorpion can) is something I haven't given much thought to.