>I've always preferred to have those types of discussions in person with some whiteboards available for fleshing out ideas.
Not everyone has people to talk to in person that understand their subfield. In a small institution it might be 100 miles to the nearest person who could converse fluently in what it is you're thinking about, even if thousands of them exist.
That's a great point. In that case, I would prefer a video conference call or an online service that allows collaborators to share a paint canvas or some other kind of unrestricted drawing board. Again, this is personal preference, but I prefer text for writing out proofs and something visual and more freeform for brainstorming.
Not everyone has people to talk to in person that understand their subfield. In a small institution it might be 100 miles to the nearest person who could converse fluently in what it is you're thinking about, even if thousands of them exist.