BC,
It isn't for adding draw weight but to help keep splinters from lifting, knots from giving away, grain runoff from creating havoc and such issues that would work to kill a bow. And, is good for giving a good canvas to paint upon.
After looking at cow rawhide a couple of summers ago and seeing how thick it is I made my own from deer I have harvested. Much thinner and lighter. I've read where some have used cow rawhide but sanded it down thin first.
I've, yet, to use it on a bow I've made but will in the future. Recently, I had the opportunity to handle a beautiful rawhide backed hickory recurve made by John Booth. It was very appealing but it did not prevent set in the limbs.
Hope this helps.