Sweeping - Only occasional success

I'm getting rid of a lot of old apps from my computer. I have Hazel set to sweep each time I delete an application. It finds supporting files, associated plists etc about half the time, but the other half, it reports nothing, and I have to search with Spotlight. I can find them easily, but Hazel can't. Why is this? Right now, Hazel is of little use to me.
I thought perhaps I needed to Fix permissions. I'm doing that now. If it fixes the problem, I'll report back.

Well, fixing permissions made no difference.
For example, I have just trashed 'Resorcerer 2.4.1' and Hazel reported nothing. I search myself and find:
com.mathemaesthetics.resorcerer.plist
Resorcerer® Preferences
(Both in /library/preferences)

This is happening often. Seems to be with applications that I haven't used for ages, or hardly used ever, but that is precisely the kind of application that I want to trash.

I presume that Hazel is much more efficient than this, and I am doing something wrong, but I don't know what it might be.

You need to check the logs to see what is happening. Check the sticky thread at the top of this forum about turning on debug mode.

My guess is that you have another copy of the app somewhere. Hazel won't prompt to uninstall files for an app that is still installed somewhere.