[uallo]

The group of people that go through the hassle of signing up and setting up everything again to avoid paying is probably equally small. If the account setup is so frictionless that a lot of people do it again and again, you should work on adding benefits to loyal accounts instead of banning new users.

[8organicbits]

You can actually check how many users it impacts by watching how the bounce rate changes after a user with a disposable email address is told their address isn't accepted. Adjust course based on your metrics.