When everyone's in the office, I can _see_ when they get back to their desk and haven't gotten into anything again. I can see that my question isn't going to interrupt them.
As it stands, I interrupt everyone and they interrupt me. I haven't been able to get into flow during office hours in 18months.
Code review discussions which would take 5 minutes take 3 days. You have to write multiple paragraphs instead of walking over and saying "dude, look at this right there, like _seriously_."
Nothing like a little pair programming to work through a code review.