Are clean installs necessary?

[TSE]

I'm going to go the legitimate route of getting all my programs for this school year, so if I uninstall all these programs and install the new versions of them, will the old versions leave anything behind?

Is installing a clean slate of OS X, even when upgrading say from Mavericks to Yosemite, ever necessary?

 

[psik]

I'm going to go the legitimate route of getting all my programs for this school year, so if I uninstall all these programs and install the new versions of them, will the old versions leave anything behind?

Is installing a clean slate of OS X, even when upgrading say from Mavericks to Yosemite, ever necessary?

God may say necessary, I say very recommended, so it's close to necessary if you want to play it very logically.

 

[Weaselboy]

I'm going to go the legitimate route of getting all my programs for this school year, so if I uninstall all these programs and install the new versions of them, will the old versions leave anything behind?

It depends on how you uninstall them. If you just drag the app to the trash, then yes there will be all sorts of support and settings files left behind. You need to search the drive for those files and remove them.

Is installing a clean slate of OS X, even when upgrading say from Mavericks to Yosemite, ever necessary?

There are proponents of clean installs here, but I am not one of them. If your system is working fine now, a simple upgrade to the next OS version will normally be fine.

When you see issues is with software version conflicts with the new OS. This seems to happen more often with odd utilities that regular applications. For example there is a utility that makes the menu dark colored and people that were running that utility in Mountain Lion and upgraded to Mavericks had all kinds of lockups until they figured it out and removed that utility. A clean install would have solved that issue.

But beyond a conflict like I described, IMO a "clean install" is a big waste of time.

 

[satcomer]

I tell even long time OS X users that after an "upgrade" I urge them to use the free program EtreCheck to see if an old service is running that is not compatible, then you could manually delete that old service.