Electrum wallet - Can someone explain "use change addresses" and priority vs privacy

[RonPaul2008]

In Electrum Wallet, click on preferences, it gives some options:

1. You can choose "use change addresses" "use multiple change addresses" or choose neither.

What exactly does this do and is it important?

2. There is a choice of "priority" or "privacy"

What does this do?

Thanks!!!!