In our neck of the woods, the SAT is still the norm. People sometimes take the ACT, but often that's because they heard somewhere that some people do better on one than the other, etc.
First thing to know is, through three test takings, you can take your highest math and your highest verbal score and add them, even if they came from different sittings. If you take the test a fourth time, however, the scores start getting averaged. You should therefore understand that you should never have a plan that involves taking the SAT more than 3 times, if that.
Second, it's not helpful to take the SAT as a sophomore. There are too many things you'll pick up as time passes, so your early SAT score is almost certain to provide a sub-par record for you. That is, you'll spend one of your three sittings just to get disappointed.
The PSAT is a decent tool to use as a predictor of what your SAT's will ultimately be. This will help you get an early read on whether you are truly Stanford or Ivy material. Unfortunately, we live in an era of rampant grade inflation, so for many students, the test scores are a rude awakening that all those A's they've been piling up don't necessarily mean that you've been learning at a high level. If I hear one more person say, "He's just not a good test taker," I'm going to scream. (Daniel Tosh has a wickedly funny joke about that old saw.) The problem is not with his test taking. The problem is that at our local high school, 20+% of each class has a GPA at or above 4.0, and a 3.4 puts you into the bottom half of your class. The NCAA still credits those grades as passing muster for eligibility, but that doesn't mean Stanford or Princeton are going to be able to get you through admissions.
We do require that our players take the SAT in March of their junior years. This assures that we have actual numbers in hand before summer play starts at recruiting venues. It helps us to advise players on where they should and should not be looking. If the player would need a higher score to get into his goal school, this early score lets you know whether it's reasonable to hold out hope for improvement upon re-testing in October of senior year. With an intensive review/prep course, it's reasonable to hope for improvement of 100-150 total points on the two-part total. On the other hand, if you want to go to an Ivy but you have a 3.8 and a 930 score, it's time to revise your list of target schools.
I honestly believe there are schools out there to fit pretty much any player. The key is to target your recruiting efforts towards reachable goals. To do that, you have to have some objective data to work with.