... says a recent Nature study because people look at each other more, instead of focusing on the task at hand.
On the other hand, picking "the best idea" from a pre-generated list is done more effectively in online collaboration.
Take-away, don't use online meetings for brainstorming.
Caution is that deciding the quality of an idea is inherently very difficult and the quantity doesn't always mean more since power law is in effect i.e. Mona Lisa so this study has some bias too.