gives me the chance to talk to the other parent first
removes any unwanted pressure from anybody involved who doesn’t want it, but might feel pressured into saying yes because they’re already there.
most importantly. I (the adult) want to make the most of you (the child) being out of the house. I could have gone out to dinner, thrown a grownups party, etc.
This was specifically a rule in my house. If you ask while your friend is there, the answer is no. It had to be prearranged.
damn, I always remember how exciting it was to have a spontaneous sleep over.
Why?
So many reasons.