I actually do not recommend formula sheets, except just as a refresher. Perhaps take it with you if you are going somewhere where you can’t study a book, but want to spend a little time reviewing, like the waiting room in a doctor’s office or something. Reading is much more important, because if you can read 3 pages about the meaning of one formula, and truly understand how the formula is derived and how it’s used, it will stick in your mind extremely well. I didn’t refer to the formula sheet from Schweser once for L1, and I never had any problem memorizing any of the L1 formulas.
Bottom line, formula sheet is NOT a substitute for reading the material, and I would say it doesn’t help at all, unless for some reason you are unable to read the book at whatever particular time.
Also, what lemiman says is best, if you want a formula sheet, create your own. Again, it will stay in your memory much better.