I fell once while putting up a hang-on treestand. It was homemade and part of it failed as I put weight on it to get it to bite into the tree. I completely feel I was so very lucky back then. I always used a waist strap I made while in the stand but never considered one while setting things up or climbing the tree. That waist strap I made likely would have cut me in half had I fallen and really was really only used for stability, not keeping me from hitting the ground.
Nowadays I always use a lineman's strap to go around the tree to my harness while setting up hang-on stands. It is surprising how easy that strap makes it for you to actually climb and use both hands while setting stands. Simply put if you haven't used one for setting up you simply do not know what you are missing. Once those kinds of stands are in place I always have a Lifeline to install for the trip back down. I will not put one up without it and I have extra's now in case I need to replace one.
Climber treestand I always use a strap around the tree attached to my harness, all the way up and all the way down. This is literally one of the easiest ways to stay attached to the tree 100%.
Ladder stands can be a little tough to get strapped to the tree without some risk during set-up. Once they are up I feel they are definitely one of the most safest and stable ways to get up above a deer. That happens when I install the Lifeline in those as well.
There really are no excuses any more when it comes to adding safety equipment and a good harness. I have made it mandatory on our property that if you hunt from a treestand you MUST have a harness on and use it properly, with the aid of the Lifelines as well. If not you will not be asked back to hunt, period. I've heard the complaints (and I used to also be one that complained) from people in the past of not being able to move or get into position for a shot in certain directions. Oh-bucking well
buy your own property and do as you wish there.