Resting is the passive half of every trade. You wait, you may earn a rebate under maker-taker pricing, and you buy below or sell above the midpoint — but you only trade when someone chooses to trade with you.
That choice is the cost. The flow that reaches a resting order is disproportionately informed, which is adverse-selection: you are filled most reliably exactly when the price is about to go against you.
Example: you rest a 1,000-share bid at 30.00 for two hours. Nothing happens while the stock hovers at 30.05. Then a seller arrives, you fill at 30.00, and the stock is 29.92 twenty seconds later. Your $50 of theoretical spread capture is an $80 mark-to-market loss.
Related: working-order, adverse-selection, queue-position, liquidity-taker