I generally advise clients to wait until after we have had a number of lesson before taking the SAT/ACT and subject tests. For example, I had a client with 1120 PSATs take the SAT after 20 hours of lessons and a similar amount of homework. The student got 1280 on the first try of the SAT. I know they superscore and so on, but it looks better if the schools see a good score on the first try. A big increase would look like the student was doing preparation.
I don’t understand the point of your post. Surely everyone should take the tests after doing preparation? Do you mean people should NOT take tests if they haven’t prepared? Seems like common sense.