What exactly is the purpose of Gsettings? Do I need this?

Accordingly to the documentation, GSettings is:

GSettings are a nice way to manage your application’s settings. Those settings are stored in binary form for fast retrieval, and can be manipulated outside of your application as well using specific tools.

That tells me a lot but at the same it doesn't tell me nothing. Do I need gsettings at all? What apps are using this? What is the difference between gsettings and glib2? What do I have a bunch of schemas for software that I don't even have installed? If I run gsettings list-schemas I see schemas of apps that are not installed in my computer, that is very annoying.