Comma use: essential or not essential

Hi. I don't see how a decision can be made as to whether to place a comma or not in situations like these. Can you help? In situations like these, I mainly try to find out whether or not they are essential to the overall meaning of the sentence, but it seems hard to decide.

1. It is the same as a passbook account, except depositor receives statements instead of a passbook.

2. XXX is a public service, which catalogs over XX consumer resources.

3. Factors that determine the dollar yield on an account are? usually based on minimum balance requirements, or transaction fees.