Depends on your limits and your looseness.

Limits: At upper limits (15/30, for example), the rake is very small in relation to the pot, so your percentage rake is much lower. The rake is still capped at $3 on those tables, but the average pot is usually in the $240 and up range. 3/240 = 1.25%. Compare that to, say, a 5/10 table with average pot of $75. 3/75 = 4%. At lower limits, you're essentially paying 5% every hand that isn't folded to the BB.

Looseness: Playing more pots = winning more pots = paying more rake. The more you trade money back and forth, the more opportunity the house has to take money off the table.