This is one area where, IMHO, Macs lag.
Yes, in many cases (if not most) you can delete an application by dragging to the trash with no ill effect. So what if some prefs remain? They're small. And ditto with many other support files.
But not always. And in fact on some occasions you may be deleting an application because it's causing problems or not working correctly, so you may definitely want to get the prefs and maybe caches.
I have found AppZapper to be useful in the situation where I want to get the prefs and maybe caches; it's like most application removal utilities. But it's just a matter of convenience: some applications have prefs that are easy to find, but if you have a bazillion applications, and the name of the pref is com.obscure.prefs for the application SomethingElse, it helps.
A well behaved application will have an uninstaller, particularly if it's running around installed kexts or whatnot. Most uninstaller general utilities, however, don't go that deep. They won't find all the caches, frameworks, BOM files, receipts, fonts, etc that a problematic program installed. And some of the programs that cause problems are precisely the ones that require you to remove every speck of their existence.
And sometimes the issues relate to licensing and copywrite management; developers do stuff so you can't pirate. But then it gets hard to find what they installed that's preventing you from upgrading or running a program. I had huge problems with that and MS Office, and even with Apple's iLife stuff. No installer utility helps with that, unfortunately.
So yeah, an unintaller utility can be convenient. But you still need to use the application's uninstaller first, so save it if it came with the download, or look online for it. And learn how to manually delete stuff; you'll probably need it someday.
And tell Apple to have a pref pane for doing it. The days of pretending you could just drag all Mac applications on and off floppies is long gone so stop pretending it's that easy. Even Apple's support has to run a long KB article on how to remove pesky iLife applications by manually going into prefs, and even into the Receipts folder (which of course they hide by default)[ts3249]. Sheesh.
