If it's a carbon bar, you do want to be careful... not only when you're snipping the ends off the grips but also with the clamp design of the barend and the amount of torque you apply. Many CF bar manufacturers have some tech docs to help you out with determining which clamp designs are compatible with their bars and possibly even proper torque values. You can also get some special anti-crimp plugs or reinforcement rings that slip inside the bar and prevent the clamp from crushing it when you tighten down the clamp.

I personally run my barends a little loose so that in the event of a crash, they will move instead of snapping off the tips of bar.