Most really don't have a clue and to be honest neither do I.
I know the controller has to maintain sparation. Either visually from the tower or by other means.
I know you can't get VFR in controlled airspace at night only SVFR
You need SVFR if you want to go into class A you can't get VFR
You can't get SVFR for crossing airways unless you can con a mil controller into it.
If a controller clears you SVFR read it back continue looking out the window and don't hit anything.
Thats in the UK, other countries its different and best not gone near in my experence if you have the option of an IFR clearance.