Board Thread:General Discussion/@comment-24749544-20140329111822/@comment-5398287-20140329203416

The only instance of that not being counter-productive is when Koga manifested Muramasa with a special ability of his Zanpakuto, since that was very quick and didn't require concentration. But again, filler arc, so unless that's the ability of a canon Zanpakuto (it MIGHT be Yachiru's, in a way) there's not much likelihood of it happening.