Just a warning for anyone that may accidentally enable this and forget. I noticed a significant decrease in range on a WRTSL54GS with this option set to manual. Computers downstairs (router is upstairs) would not maintain a stable wireless connection. I lost some hair figuring this one out since I had forgotten that I had enabled the option.
Oh, of course. I just switched my WRT54GSv4 back from OpenWRT and was noticing the same problem… I didn't think to experiment with this setting and left it at the default (which is one of the "on" settings).
Turns out the driver it was using in OpenWRT doesn't support interference mitigation, so it must have been off.
Thanks for the heads up!