Most of my serious mountain backpacking has been done without pliers. I either carried a light folder or a SAK with scissors and saw.

Pliers are primarily helpful in fixing the modern gear we take into the wilderness. The gripping power helps when fixing stoves, sewing failed zippers, repairing ski/snowshoe bindings, and fixing D-rings/hooks on boots for example. This is especially true when travelling with a group of young people who are using old/donated gear.

Other useful camp tasks for pliers: handling hot pots (esp. on fires), pulling stubborn tent pegs, and loosening knots. But there are ways to accomplish all these tasks without pliers too.

I can certainly see the value of pliers and a good wire cutter if you're hiking with a dog. Some areas have abandoned fence wire (or snares left by unthinking boneheads). I have also removed porcupine quills that weren't in deep (highly unpleasant for all concerned). And pliers are great for breaking up ice balls that build up between the toes in certain snow conditions.

With all that said, if I were to get back into long-distance backpacking, where every ounce counts, I would probably go back to the lightweight folder and SAK. Odds are I could add a tiny pair of hobby needlenose pliers and still carry less weight than a Wave-II.