With selfbows and wooden arrows in most of my situations here in Pa, stillhunting, I generally like to get within 20 yards or so of deer, but have taken them as cleanly as any I've killed out closer to 30.
I like to get closer to smaller, quicker animals like squirrels, rabbits, groundhogs, etc.
That said, it isn't a distance thing for me so much as it is a feeling when everything comes together, and it's time to pounce. I guess I've done it enough that recognizing those highest percentage shot opportunities happens without much conscious thought. If I have to think about it much, or 'force a shot' even a tiny bit, I hold the string.
I may pass one at 8 yards and kill the next at 25.