How effective are email return receipt requests on the Internet?

When people ask to receive confirmation of delivered emails through MS Outlook, how effective is it if many people are not using Microsoft email products? Do other email clients respect the request for a receipt?

How effective are email return receipt requests on the Internet?
Yes, most clients respect the request, but unfortunately users don't (I'm one of them: I click "No" on all requests I receive. I think many people send them because they don't know how to turn the option off, so I prefer to ignore them).