The reason they allow various drive letter assignments is so you can use them.
In my experience assigning each drive to a different drive letter and leaving them alone (still connected) is most reliable.
If you disconnect/re-connect drives the letter is prone to change .. but simply knowing that makes managing them much easier.
I'd rather they shutdown when not needed and keep the drive letter assignment .. but that's just my POV. So I leave them connected/reserved whenever I can.

I do not work here, but the benefits are still awesome
Make your sound your own!