pros: you get to be with them every day.
you can do things together all the time (same schedule, etc)
you have the same circle of friends most of the time
cons: same as pros. only that you'd look at it the negative way. like you'll get bored being with them everyday.
you do things together all the time that even if you don't feel like doing so because you have had an argument or something
you have the same people who knows you that might be a cause of argument or issues.
it really depends on how you look at it. some friends i know don't want to be in a relationship with a workmate