The big advantage comes when the URL is public somehow - like with git submodules. The http/https URL works for both read-only and read-write users unlike git:// or git@ URL's.
The disadvantage is that http/https can only be pushed to by users who have git 1.7.
a lot of times ill work on projects on the way to work and then i would like to do a push when i get into the office in the morning, assuming every thing is working :). However ssh to non-local machines is blocked at work. there are ways around it using special vpn profiles and the like, but this looks a lot easier.
All I can see is being on a foreign computer. When on a foreign computer I generally don't even have git so why bother.