As Jerricho pointed out, there is an azimuth error inherent in TCAS (30 degrees iirc).
That's where the danger lies in using TCAS to 'identify' target aircraft.
But with the additional situational awareness afforded by TCAS, when the aircraft pops out of the clouds and traffic is seen, wouldn't the crew then be entitled to call visual ? provided they give a range and bearing to target aircraft that checked with the radar information ?
Does this example save RT loading by obviating the need for further traffic info ? after all, standard separation is still applied till the aircraft is visual.
Maybe 'we have him on TCAS' , in some cases at least, means we'll keep a look out and call you when we're visual.