>>289995137
Working in Blender alone for 8 hours can get really lonely. Doing things together with other people is fun, who would've thought. 
You can also ask other people questions on how to do something and they might be able to help you out, and you them, because maybe someone is good at texturing, the other person really good at shader stuff, a third person spent years exporting from software X, another person is great at audio or particle systems - but no one is good at everything.
Add to that that you can directly stream a Blender window to get realtime feedback.