question about applications

I'm not entirely sure but I would guess that different apps have different ways of communicating with the system. You'll probably get some better responses shortly.

 

Most apps are self contained, that is the thing you download is the entire app self contained. More complicated apps may need more components, hence they often use an installer.

 

^ ^

see!

 

Most applications create folders for themselves in places like Preferences and Application Support the first time they're run; others might use an installer to create these folders (and perhaps populate them with data files the application needs) before the first run.

Some applications delve into, or alter, the way the system works and need to insert their own code. They might need access to system folders and files that require an administrator password; by providing the password on install, maybe you don't have to provide it every time you run the application. There's any number of reasons.

When you delete an application, if you delete only the application package, the preferences and whatnot would remain where they were (unless you used something like AppZapper). An installer often also provides an UNinstall option, which (ideally) would remove these files for you when you wanted to uninstall the program.

If you pick the name of an application you use and run a Spotlight search on that name, odds are you will find .plist files, prefs, perhaps a license, perhaps crash logs ... while all those are probably created by the program as you use it, they might also have been placed there by the installer.