Possible validation:

* visited a page

* signed up for a waitlist

* paid you money

The further down the list you go, the more commitment you have, but the fewer people who will be willing to give you that commitment.

A waitlist is a nice option in the middle, plus it gives you a way to reach out to interested folks if/when your project is ready. It costs you approximately zero too.

I think that is the main reason you see this so often.

Once in a while we hear a story like Google using a waitlist for gmail but I think (1) 100% of the people who sign up for a waitlist are enthusiastic right now, but the fraction of them who will still be enthusiastic when your product is available to them will be less than that and (2) if the product is available now the odds are 100% I will be able to try it out, but if there is a waitlist the odds are less than that that it will become available to me and weighing that I decide not to join. (I did sign up for the Bluesky waitlist, I did get an invite eventually, but I did not use the invite because life got in the way and wound up signing up after it was open to the public)

That judgement might be wrong if it is part of a bigger marketing plan. If you have something to say about your product that is really interesting to somebody other than you and you plan to run a regular newsletter about it, that might be a good idea.