assume you are flying level and you get RA to clb, if you do clb without putting your fds off A/T will power back till you hit vls
at which point a lot of nasty thing happen
above given example is only one of many
I am sure you get the drift......with fds off A/T will be a slave to speed so one less thing to worry about. forget all the gizmos in front of you and concentrate only on your V/S and listen to the aural warning till you hear "clear of conflict"......least you end up upsetting the entire stack of...c's