Don't really need them any more. ECM has been modified with standard socket.
Very nice for quickly dialing in a TBI setup, can make realtime changes, run different .bins for different situations etc.
Eliminates the need to swap/burn chips while tuning.
Make change(s) on the fly while driving don't like it, didn't do what you expected, simply change it back.
Can hold up to 8 tunes, one for better MPG, one for towing, one for high altitude, one for smog testing, etc.