The four divots on top are where the feet of the piece above rest, so a stack can't slide around ("dimples", "dents" — same thing). Smooth top is only for the top row of your setup, if you prefer that look. Every piece ships with feet on the bottom either way, so "smooth" only changes the top. When in doubt, go divots — it's more flexible. If you plan to expand later, order divots now: you can't add divots to a smooth cube after the fact (they're CNC cut). Or order smooth now and, when you add a row, buy the new cubes with divots and slide them in underneath the smooth row. The same divot/feet system is shared by Storage Cubes, Stereocabs, CD/DVD Cabinet, 45 Cabinet and Browser Bin. Partial divots (one side only) aren't offered.