Many bow hunters simply drop their bow arm to shoot when up in a tree stand, I used to do so myself...There are many reasons for this but I think a major reason is that some don't wear a safety harness and want to feel the trunk of the tree when they shoot...
When you simply drop your arm and don't bend at the waist then you also have a tendency not to bend your neck and get your nose down on the string at full draw...In effect, this is raising the rear sight which makes you shoot high...I cringe when I hear of guys having to shoot under a deer to hit it, many think the deer is jumping the string when it's actually their form that is making the shot go high...
It's best to have 2-3 rear points of references...I shoot fingers and do not use a peep...I find that I shoot best without a face mask because I use the corner of my mouth as an anchor...I also make sure the string is touching the side of my nose and I line up the pin within 2 nocks that are on my bow string...By using a full body harness I can bend at the waist to line up with the deer and don't shoot high...
As far as jumping the string, only shoot at relaxed deer...Too many less experienced deer hunters shoot at deer that are already suspicious and are ready to bolt at the slightest noise...
They aren't really jumping the string, they are simply crouching to get that first leap...