Often over in the #fedora IRC channel, we have people who come in with some issue or problem who only spend a minute or two gathering information on it before asking: "Should I just re-install?". Sometimes they mean re-installing the application/package, and sometimes they mean just reinstalling the entire OS! I fear this is a ingraned reaction from the closed source software world where there is really sometimes no way to tell what the application/os is doing and returning it to a clean state is the only choice. Thats not (usually) how things work in the open source world though. :)

1. First ask yourself: Did this thing work before? It doesn't now? What changed? Check /var/log/yum.log or other history and find out exactly what changed. Did you change a setting? Did you upgrade a package? You can think look for how to revert that specific thing that caused the problem. No need to re-install.
2. Do you have reason to think the package or application was messed up somehow on your disk? ie, do you have disk problems, or did you run a script as root that might have messed up binaries? Sure, then a 'yum reinstall package' might be in order.
3. Does the problem/issue occur with another newly created user? If not, then that points to a user specific setting. Reinstalling the package won't do any good, because the setting is tied to your user. Instead look for what that setting is or how to revert it.
4. Is the problem/issue causing you to not be able to boot? Instead of re-installing, look to a rescue media. You can often fix the issue by booting 'linux rescue'. No need for a re-install.

About the only time you should absolutely re-install your OS is when your machine has been compromised. Otherwise, it's a lot better to fix the real issue, no only because it's often easier, but because you will learn something in the process!