It's hard to say which ones you are talking about also without some pics for reference.
Sometimes like Immortal-D said it could be good.
In other cases you could be making one simple v-vis 'cube' into a bunch of small ones with a badly placed nodraw brush. in which case there are more leafs that serve no purpose. That would be bad.
For example. If you are in a displacement canyon shaped like a U, but maybe has a ledge along one side.
The no draw under the whole canyon could just be 3 brushes to seal the void. There would be a large gap of nothing under the ledge, but putting nodraw there just to fill in that gap would split the leaf of the canyon up but you'd always see the whole canyone anyway. So why split the leaf?