Good add-ons and bad add-ons
Every module that is part of the core of Moodle has gone through a thorough quality assurance process. The potential problem with third-party add-ons is that you don't know anything about the quality of the software.
While it is possible to uninstall modules if they don't fit your purpose, you will have to make sure that you don't put barriers in place for future updates. If an add-on is not maintained, it is unlikely that it'll be able to support any upcoming versions of Moodle, and you will either have to delete the module that's already in use or you won't be able to upgrade your system. Also, a module might cater to some required functionality but can also compromise the security of your system.
There are a number ...