uninstalling manually removing all files

I know to uninstall stuff you simply drag it to the recycle bin.

I've got AppZapper however there were some programs I uninstalled before I installed AppZapper.

Where to I look to ensure all files from previously uninstalled applications have been removed??

I usually look in:

youraccountname>Library>Application Support
youraccountname>Library>Preferences

and also in:

YourComputerName>Library>Application Support
YourComputerName>Library>Preferences

There may be other places and someone else may post them.

How is AppZapper, I wonder if it's worth getting, would be interested to see the files it finds to delete...