This article may be of help to you:
The full article on scope can be found here: https://community.tealiumiq.com/t5/iQ-Tag-Management/Extensions/ta-p/13649
However here is a TL;DR version
The other scopes are:
Additionally, for All Tags Scope, you have the additional options:
In addition, there are also Run Once options for these, whereas the name suggests these will only run once.
I hope that helps explain Preloader and scopes in general.