After decades with Windows and Registry issues, now I have a MacBook Pro (about three weeks). Reading this forum, Onyx seems to be a popular, even the most popular, maintenance utility. My question: Does dragging a 3rd party app into the trash actually get rid of all the files associated with it (unlike Windows, where Uninstall rarely removes ALL the files associated with an app)? If not, does Onyx perform that task? If not, does it matter with a Mac; I mean is this an issue on a Mac? Thank you. (I wish I had switched years ago.)
Most 3rd party apps have at least a preference file that gets left behind in your user Library. These are no big deal, take up little space, and can be safely ignored. Many have other helper files and such elsewhere that may be in the user or root Library, and may or may not impact your system by being there. There are several apps, free and not free, that purport to help uninstall and root out files that get left behind. Onyx is not one of them, though it is excellent for what it does do. There are a few uninstaller helpers to recommend, though I will say in advance that NONE are absolutely thorough.
AppTrap sits in the background and watches for any apps that are dragged into the trash. It will then prompt you to move the associated files as well. It's free and relatively effortless.
TrashMe is an app that you have to open first, then drag an app you want to delete onto its window and have associated files scrubbed. It's free and while it takes a little more work to use than AppTrap does, you won't be pestered by pop-up dialogues when you might not want to delete the support files (say, in the case of upgrading an app).
There are a number of other for-pay apps that do the identical function to TrashMe (AppZapper, AppDelete, to name a couple). The last time I evaluated all these, none of them do anything different.
One key limitation to the above mentioned apps is that they only seek files for the user you are logged into. If you have multiple users using the apps, their support files will NOT get deleted. Not last I looked anyway. The only one I know of that does a more thorough job is
TinkerTool System. Its Uninstallation Assistant is the best I've seen, though it too is not absolutely perfect. It also does a lot of the things Onyx does and has a couple tricks up its sleeve that I've not seen elsewhere. It's not free, but pretty reasonably priced.
Also worth mentioning now… a couple apps often brought up here are CleanMyMac and MacKeeper. Most the regulars here, myself included, recommend avoiding these like the plague.