If you are short or longsighted then you can use the focuser instead of your glasses. However the focuser cannot compensate for astigmatism or any of the rarer eye defects.
I use the finderscope with my glasses on and observe with glasses off.
Though more and more I'm observing using the Gstar-ex hooked up to the scope or tripod mounted and view via a CCTV screen. Easier on the eyes.
It's a right royal pain to get the focus correct for astrophotography when what you see isn't what everyone else sees.
I see your point guys, when I focus for astro imaging i use an angle finder on the Canon 5D, and always figured that because i wear glasses i would still have to use them when doing that task, but it matters not, it focuses fine either way.
I have a Tele Vue -0.75 dioptre astigmatism adjustment lens on order so that I can stop wearing my glasses at the scope. Supposedly it will matter for me the most with eyepieces longer than 20mm focal length, based on my scope focal length. Right now, if I want things sharp, I do have to wear my glasses.
I observe with glasses off. The Telescope focuser works as my glasses. Pity my glasses didn't have a focuser so I could see things close up when I have them on
Being short sighted, without astigmatism, I much prefer to observe without my glasses. Not only is it more comfortable, but I figure that the less glass in the optical path between infinity and my eyeball the better.
I always have them with me, though, because in any observing session I spend as much time looking up at the sky naked eye than through the eyepiece. So it is a case of, "On again, off again" for me.
just thought i would share that piece of useless info with you 
