TCAS is designed to highlight conflicts, alert the crew and display a position to assist the crew in visual acquisition of the target. The closer you get to a conflict the more accurate the picture becomes, at range its not highly accurate though. However should you fail to sight the target and it gets too close, the unit will give a resolution to avoid. That's when it starts making lots of noise, things turn red etc... It is not designed to be a quasi radar scope, you can't say for sure a target is X aircraft as it does not display enough information. However that said, you can see stuff at range and then get an idea something is out there and try to communicate with it, so for situational awareness it is pretty good. I'd still separate by a safe margin altitude, track, distance, but you can use TCAS to see when something passes, then talk to it to get actual position to confirm clear. That then relieves constant position updating and radio clutter. eg " XXX I'll maintain 6000, you stay at 5000" then watch it pass on TCAS, "XXX whats your current Distance and track", (XXX responds with a GPS distance and track away from you), "XXX all clear, see ya later" or whatever.... Good thing is if either party stuffs up the TCAS will show it happening and you can query them and get ready for avoiding action.