I think there is a benefit to doing at least one full length timed mock SAT (and then doing the post mortem where any wrong answers are reviewed).
And being familiar with all the directions and what they really want and which formulas will be provided...I think the princeton book (well at least the one in the 1990s when I was teaching SAT prep at a study center) was the best one for teaching you to be very familiar with the directions (don't have to waste time on them) and knowing more information about the test (helpful for overthinkers).
