I normally don't use one when I hunt private ground, which is about 90 percent of the time. I find that it's harder for me to get my bearings with a flashlight because all I can see is what's in the narrow beam of the light. I can't count the number of times I've walked by stands while using a light. I can usually walk right to them without one. I haven't really noticed that I make any more or less noise without a light.
If it were a particularly dark night and I was on unfamiliar or public ground, I'd use one though. I also use one when I know I'm going to hit rough ground, a washout, or a blow down. No sense taking a fall that might end the hunt.
Deer could care less if you use or don't use a light. I don't even think they pay that much attention to the noise of you walking in. There is almost always something crashing around in the woods at night...usually other deer. I've set in the stand in the dark and heard deer, cattle, etc. making quite a racket. Yes, deer step on and break sticks too. The light may actually be an advantage in walking up on them because they can't make out your form behind it. If they smell you or you get close enough to them in the dark for them to make out your form, which they do a lot better than we can, they are gone.
There is a reason why it is illegal to hunt deer with a light: it works!