Maybe, maybe not. From what we have seen so far he doesn't need too
I agree with this--or, at least, it wouldn't be as effective.
1) He used nine-tails mode when fighting six tailed beasts, the ten tailed beast & then along the other 8 against Madara. When it was just Tobi he never went full size.
2) His hand has to touch Kaguya--if he's a huge mass of chakra that won't be as easy; it's best that he stays small and fast
3) Freaky Bhijuu mode is a huge mass of chakra--JUST a theory, but it might make him vulnerable to getting it all sucked up.
4) He's using shadow clones to keep Kaguya confused and off balance. With one enormous tailed beast running around he'd be saying "Here I am! Shoot me!"