Paying attention to things like the weight of water bottles can easily result in weight savings of ten to twenty pounds. Over the course of a week long trip that is considerable.

I first became interested in lightweight, serviceable gear doing SAR. Cutting weight allowed me to carry more items of use in the operation- everything from rope to stethoscope to additional dressings, IVs, etc. So yes it can be (at least in theory) a matter of life or death. I always got a haircut, as well. Don't forget to trim your fingernails....