Any reason to unplug a wireless charger? Also, can it damage a clear case?

I got the Samsung wireless charger (not rapid charger) from wal mart for . I just got it set up, and the instructions say to unplug the charger when the phone is charged. Is there truly a reason to ever unplug the charger or is this just corporate precaution to avoid a lawsuit? lol

Also, I have a clear UAG case on my Note 5, is there any way the wireless charging could damage the case?

One more question, whats the deal with people saying the old wireless charger doesn't work with the note? Doesn't any Qi charger work with any Qi device? I don't understand what issue it could cause.