Not good enough, that can mean you rebase changes that someone else has based further work on (but hasn't pushed it yet, or has pushed it to a different branch).
> Why are you having people base their work off your in progress work?
To collaborate more closely and reduce (or get ahead of) conflicts. The whole point of using git at all is to be able to base your work off other people's in-progress work; if you're not interested in doing that then Subversion works better.