I was thinking about this myself recently.
Quite a few of my users tend to use the product a few times. They need it for a specific project then once they have done that project they don’t need it again.
I was tempted to try lifetime licenses for this reason but as others have said it can look a bit desperate.
As a customer, I bought a lifetime license for one of the live chat apps the other week but the quality of the product is not great. Their mobile app does not work at all and support does not seem to care.
I do worry that the business model of a lot of these SAAS companies could be sell loads of lifetime licenses and then disappear.
The groupon comparison is a good one, it was a disaster for many businesses.