Should I get insurance when mailing package with USPS?

USPS offers insurance when mailing packages, but I’m wondering how I’d even file a claim if they lose it? Would I need to show a receipt? Most times I don’t have one. Will they accept other ways to prove value? If not, why bother with the insurance?

If it is something of value maybe consider using who jewelers use UPS or FedEx.
Uncle Sam has a way of weaseling out of even their own rules/codes.

If the $ value is more than what is automatically provided, yes. Filing a claim is easy.

Yes. I have mailed three certified mail last year. Of the three mailed, USPS never showed any of the three were delivered and tracking was lost at distribution center! One was IRS recipient.
I learned to charge each transaction on a separate credit card transaction. Now I dispute USPS failures and get the credit card to reverse the charge.