Like Squirrel, I let lots of deer walk, as well as other animals over the years, if everything wasn't absolutely the way I wanted it. I hate guys saying, especially the pitiful crop of TV mush, "I think I got a good shot." I've bow hunted for over 55 years, and, I suppose way back in the '50s and '60s, I may have taken shots and thought that, but today when I release an arrow I don't think, I know I've taken a good shot. I play the game different than the question posed: instead of asking how far, I work hard to answer the question, "How close was I when I took the shot?" In the last 20 years or so I've collected black bears, elk, deer, and an assortment of other game with bow shots well under 20 yards, placed the arrow exactly where I wanted it, and witnessed most of that game dying within my view--great tracking that way!
No easy answer to the question, but I like Squirrel's answer. Just remember to respect the quarry every time you go afield.
Best of luck, Arch