Think of revenue in two ways: subscription and transactional. Both can be profitable, depending on your product.
Subscription:
Transactional:
Revenue generation is not binary -- this can be a blend of both Transactional and Subscription.
Ex: A stock photo website that charges $20 / image, or 3 images / month for $45 monthly.
Personally, all of my freelance work is a blend of the two: upfront dev costs, then ongoing fee for maintaining the tech stack and being available for questions.
My clients are small businesses: if something is working, the client generally doesn't want to be bothered and would prefer to run the businesses. I email them each week and say "How are things going?" This has generally resulted in <15 minutes of answering simple questions, via email, each month.
Any thoughts? Please comment below!
Happy rev gen :)