I suspect they thought it would short-circuit a lot of plots - it's one thing if Picard or Riker can read the poker face of the Romulan/Cardassian/whoever on the viewscreen and guess what they're up to, it's quite another if Troi can pipe up and say "Captain, the Romulan ship have planted mines at 020 mark 120". Spock wasn't afflicted by this primarily because they range-limited him - even when his mind-meld ability was introduced, it was only over short distances, and they soon limited it further to touch-only. The problem with the character that emerged, however, was that her power was a horrible kludge of "still too powerful" and "too useless" - too powerful because she could sense deception at a million kilometres, and too useless because often they ignored this and, as everyone soon notices, just had her state the obvious - after all, if she did more than that, the plot would be over too soon. It was a simple failure of planning when they set up the show, and unlike other characters that were underplanned and didn't work in initial form (Worf, DS9's Bashir), they never really took steps to fix this. They should have depowered her, permanently, in the shuffle at the start of S2 when they moved Geordi to Engineering, retooled Worf, etc and worked from there.