Normally the TCAS climb will only be a few hundred feet, however it can be much more than that. (recently my Co had a TCAS climb over 1000ft to avoid traffic and ended up having to make a turn as the other traffic decided not to respond to their command)
You may be on a one engine out cruize, close to your performance limit. To assume that you will always have the performance to 'outclimb' the other aircraft may not be correct.
I would assume on one engine out, I would have a 100%chance of being asked to do the TCAS climb...Murphy's..
I find it reasonable to let the other aircraft do the manuovering should it be required. By turning the TCAS to TA only lets the other acft know that if a climb/decent is required, then they will do that.
IBT