Deep/Fast vs on/off

[GazinUK]

Just musing through some threads on here, noticed people posting programs that include fast/deep and wether to switch them on or off.
I've always run with them both off, as being computerized I've considered them to be a type of processing filter that could only slow things down.

 

[IDXMonster]

FAST actually turns OFF some filtering which speeds up the recovery from target to target at the expense of accuracy and slight depth.
DEEP turns ON some filtering allowing for more stable ID at depth, but the speed from target to target is reduced.

 

[woodbutcher]

I always run fast on ,deep off