They can be VERY helpful. My suggestion if you are hunting from a stand...pre-range.

Find landmarks in your hunting zone, range to them and memorize the ranges...that way when a deer comes into your zone...you'll know the ranges without having to pick up the range finder again.

Also something to do prior to the season or any old time you feel like it...
Take the range finder out with you when you go for walks or hikes...pick an object, guess the distance, and then range to see how close you are to what your range finder says. After a while you may get sooooo good you won't even need the range finder.

Lastly verify your ranger finder every time you use it or at least when you change batteries.
Measure out some fixed distances and range to them. most of todays range finders are +/- 1 yard...so they should be very close to your physical range. Note that as the batteries wear down or if it's VERY cold, they sometimes become less accurate.