I've found myself in the situation, a few times, where it was necessary to run `bundle update' to resolve dependency conflicts. You should, of course, always thoroughly test your application before deploying production code after a `bundle update', but I'd hardly tell people to not "ever" run the command, especially if you have git-based dependencies that need to be updated.
Just to clarify, you can always run bundle update for a specific gem, instead of for every gem in the Gemfile (this is the behavior if you run the command without any arguments). Recent versions of bundler (>=1.0) are pretty good about telling you exactly which gems have dependency conflicts, so it should be pretty easy to determine which gem to pass to bundle update.
