I think filters also function as a safeguard for buyers/sellers. For example if you were to place a bid to sell at $0.50 and you accidentally made a typo and entered "sell at $0.05" then the system would pick it up and save you.
Conversely, if you intended to place a buy at $0.05 and instead entered $0.50, then you'd be saved from paying the top dollar that the 1st seller is willing to sell at.
