Peroxide is both useful and harmful. We all know peroxide prevents infection, but that only works when used correctly.
Peroxide is only meant to clean around an injury, not in the injury.
A vet once told me to never clean an animalís open wound with peroxide because it kills living cells.
But on the other hand peroxide is great on unstopping a chickís plastered vent without hurting it. We have all had a chick at some time or another with a clogged vent, and sometimes when we try pulling the stuff off, it ends up pulling out the feathers and sometimes even the guts of the bird.
Using peroxide instead of water is good because it dissolves the dried up waste very easily - much easier than water. So peroxide is both bad and good for chickens and us!