If you are selling coins, putting up an ask wall is just doing the exact same thing in the other direction. And you get to absorb some of the bounce back. (Noob here, correct me if I'm wrong)
Yeah but if the market just crashed 25%, you have 200k USD of BTC on MtGox, your first thought is "Put up 1.5k ask walls at $115 $118 $120?". You're just deterring a bounce back. If you're panic selling, you'd just sell them. And within 60 seconds of the coin dump? Who see's a crash and walls up the bottom? The size and aggressiveness of those ask walls isn't from people looking to sell into the bounce back. You want it to bounce back, your BTC is worth more. The only thing they do is help keep the price down.
Here's what I was thinking:
You have a large number of coins you want to sell in a fairly short time frame. You know that every time you dump a large number there will be a bounce. You decide to sell the next segment, say 125 to 120. you can be pretty sure that after you sell that segment, the price will bounce back up.
You still intend to sell more coins. So you set up ask walls, say 500 coins, at every $.5 interval back up to 123-124. Now when the bounce happens, you sell coins to people that want to buy before the next drop.
Wait for the volume of people in the bounce to dry up. Repeat.
As I say, I'm a noob. but it seems like a way to maximize if you aren't willing to just wait and sell 500 coins a day or something.