When I first started playing the new edition of WFRP, I pretty much ignored Party Tension after reading the rules for it. After all, I feel that if I have to use something that clumsy to manage my players, I should really hang up my spurs as a GM.
However, I've found that it can be used in some more creative ways to foster atmosphere.
So opposed to adding tension when players aren't paying attention, having side conversations, or start an in-character ruckus, which I feel either punishes good roleplaying or out-of-game behavior with in-game penalties (bad), I use it to measure the atmosphere within the game (similar to the storm track cards provided in The Gathering Storm).
So if the party is in a tight spot (imagine it's a horror film, and the ominous music starts along with the very close-in camera shots), I add a point of tension. I've found that it gives me an in-game effect in parallel to the atmosphere I'm spinning with my descriptions.
It also makes the players/characters tense - if I describe an ominous scene and notch up the tension track, they start looking around much more carefully in-game, almost like they've got a sense of foreboding or the hackles rising on their necks.
I've only recently started (sparingly) using it in that manner, but so far the results are positive!
Comments, thoughts, or improvements?