Its not academic at all.
If you know that you may not be able to fly an RA, its very important to turn your TCAS to TA Only.
The reason for this is TCAS coordination. You need your TCAS to be able to let the other aircraft know that it is free to do any manoeuvre.
Bear in mind that the other aircraft may be altitude or Performance inhibited from carrying out particular RA's.
E.G. TCAS may have decided that the best solution is for one of you to CLIMB. If the other Aircraft can't DESCEND, then one solution is for it to be issued a Preventative RA to stop it climbing and hitting you, whilst you get the CLIMB.
I.E. The fact that you are getting a corrective RA does not gauruntee that the other aircraft is getting one as well. If you don't climb when directed to, then you will be in trouble.
Whereas, if you had selected TA only, the other aircraft would have assumed you were going to continue on your present path and would have Climbed.
There are many aircraft that can't manage CLIMB or INCREASE CLIMB with an engine out.
By way of comparison, what do you do for Parallel Runways Operations? You turn TCAS to TA Only, right? As opposed to briefing 'If we have an RA we'll ignore it'. The reason is the same - you don't want to take part in a coordinated encounter unless you are going to follow the RA.
Basically, TA Only is like a priority button - it makes other aircraft get out of your way. And you still do get a TA, so you can try and get a visual spot and turn instead, so you are no worse off than pre TCAS.
Fundamentally, if its in the checklist (and it is in ours) then you should do it.
It really boils down to whether you are operating in an environment where the other aircraft will have TCAS. If you are, then turning yours to TA only because of an emergency doesn't compromise your safety at all.
In my opinion, there is even a powerful arguement for putting it to TA only during an emergency descent, strange as that may seem! But thats another story.
CPB