No fly tying question is too daft not to be asked
When I tie with hare - and it is one of my favorite materials, together with CDC - I decide on dubbing according to the size of hook I am using.
For the smallest hooks (16-22) I use hairs on the ears. For medium size patterns the hairs from cheeks and for big flies the body hair. Hair from the back is dark and scruffy, good for thoraxes and rough looking flies. Body hair from belly area is finer, more creamy in color and good for smoother abdomens. When tying GRHE you will need some long hairs for the tails; you will find those between the ears and on the back of the head.
Here is a smallish (#19) fly dubbed with short & fine hair from the ears
This buzzer is dubbed with hair from the cheeks
And this nymph has thorax dubbed from the back and abdomen from belly of a hare
This scruffy nymph is dubbed only with back hair
Cheers!