Our school district pays for all 9th-11th graders to take the PSAT. Middle kid is in 12th, so she won't be taking it (I think the seniors are watching The SpongBob Movie during the PSAT).
I don't see any harm in taking it - it will give him a preview of the new SAT. Since colleges don't see your score, they won't judge him on his PSAT performance. And if he is a junior and does well, he could be NMSF (some schools offer NMSF/NMF great scholarship opportunities).
I think it is a good idea to try both the old and the new SAT. If he is a 2017, most colleges will accept either the old or new SAT with his application. If he is 2018 or beyond, take a look at college policies. Some will not accept the old SAT for HS Class of 2018 or later.
While I believe in not over-testing, I've always assumed that DS would take the PSAT.
Oddly our school will not give it to anyone but juniors. I tried last year they said they don't have the room to give it to anyone but juniors. You can take a practice PSAT in the spring of your freshman or sophomore year but it turns out that was simply a practice new SAT last year. Threw DS & I because we weren't expecting the essay. It's very very common for the top students at our school to spend most of the summer between sophomore & junior year cramming for both PSAT & SAT.
In order to take the test Wed, they gave the students the day off and teachers and in service day. Seems a bit extreme for a test that at most 50% of the juniors will take. They don't pay for it and IMO unless you are trying for National Merit it's not very important. But despite both not allowing the kids to take it in earlier grades nor all the students taking it we usually make the top school in the county & sometimes states for kids who make semi-finalists.
Yes DS is 2017 and I think it's a good idea to take the SAT this fall. Don't think we get the results from the PSAT quickly enough to use that to help decide on a Dec/Jan SAT test dates.