No, the vang can be a valuable tool then sailing upwind. Several ways actually, but here we talking about trimming in puffs using a technique call 'vang sheeting'.
To do this you get the boat/main trimmed comfortably with the desired amount of twist, and then set the vang there. Then, when a puff hits, you ease the MAINSHEET, not the traveler. The sheet goes out and the boom wants to rise, but cannot because it is held down by the vang. So it slides to leeward and only widens the Angle of Attack, just like using the traveler would. Great if your traveler is not easy to use. On boats with good travelers, it really comes down to trimmer's choice. Its a good idea to make sure your vang and boom are up to scratch, this really loads it up.