Well, it really depends on the app itself. For most programs, everything is contained in the app package itself, aside from the .plist files, which are in the Library/Preferences folder as you mentioned (keep in mind there are 2 libraries - a system library and a user library, and they may both have .plist files related to the app).
Some programs - notoriously the Office apps - distribute little files absolutely everywhere, and it's horrendous. Programs like AppZapper are supposed to automatically remove all those files, but I can't personally vouch for them.
If you're worried about space, keep in mind .plist files and other support files are generally kilobytes in size, which is negligible.