Group scopes... Say what!?

I’m scheduled to take this one on Tues the 31st (last day to be eligible for the 2nd shot!). I’m cool on pretty much all the topics except the different group scopes on different functional levels. I can memorize the group types that are possible depending on the level of the domain as well as the next guy but I need to be able to apply it. I see a bunch of practice questions where they want you to determine what kind of group to create and in which domain in the forest to create it depending on a set of circumstances (including functional level). I need some quick tips on the practical use of group scopes. I have read the groups notes on this site and they are very helpful. I just need a run-down on what scope to create and where to create it.

Thanks in advance!