Most commentary on eye relief seems to center around the eyeglasses question. I do not wear eyeglasses, but still find a couple of real advantages to good eye relief:
Lesser tendency for condensation on eyepiece - Bins I've used with longer eye relief allow noticeably better ventilation between the lens and eye/face, and therefore less condensation problems. This is especially true when I leave the eyecups down and space the bins off of my face with my brow or thumbs.
Easier to look "up" - When viewing high in the trees for longer periods, I commonly put the eyecups all the way down, and rest the tops of them higher than usual against my brow, in order to lessen the degree to which I must tilt my head back. (I can then look up with my eyes instead of just my head/neck.) The extent to which this can be done without loss of FOV depends on the amount of ER.
In the field, these advantages have made a big difference for me in certain situations. Have others noticed this?
It's just another consideration (even if you don't wear eyeglasses) for making a binocular selection.
APS
Besides optics, eye relief and eye cup comfort are major factors for me. I am selling a pair of porros as I no loger like to hold them much.
I wear glasses, and for me good eye relief is the most important point with binoculars, more important that quality of optics or weight or anything else. Personally, the best optics are worthless if after finding a bird I have to take off my glasses to use binoculars. Using bins with poor eye relieve takes absolutely all the fun out of birdwatching, at least for me.
Lew