Be careful, some strains don't really like to be topped. But, how you grow is up to you.FIMing is supposed to be a milder form of pruning, and that's how one forces any plant to grow laterally. This changes its natural form a bit. I have FIM'd my plants once, not all of them though, just to see what happened.
Of the 26 plants (13 in first stage, 14 - 1 in second stage), 6 were FIM'd, and 5 of those 6 that were randomly chosen to FIM as an experiment turned out the be the biggest, most vigorous plants. I will now FIM them all.