Depends where you hunt. In moderate to low pressure area's, you can get away with a lot.
But in extreme pressure area's, the deer are on pins and needles times an atomic bomb.
For example, my county in Michigan alone (that's county, not region or whole state) has 25,000 deer hunters, from DNR data. I'm in "deer camp country". It's rural and every single parcel over about 2 acres gets hunted, many times hunted hard.
Now, if you get 30 feet up in a tree, you may be OK without a mask or camo, but if 15' up or god forbid on the ground, you better be camo'd up head to toe, bigtime.
I've hunted in Illinois where I pulled a sneak on a nice buck across a cut corn field (to my dismay-that would never remotely happen in Michigan) and I got busted here in Michigan this fall in head to toe ASAT by simply moving my hand to the string in a very heavily covered ground blind made from about 10-15 pine tree tops. Once you've hunted whitetails under extreme pressure, you quickly conclude deer in many low pressure area's are half tame, in comparison.
In my area, fawns will often bolt in fear if not wearing a mask or face camo.