For viewing PDFs, Preview should be fine. I'm not sure if there are any other features in Adobe Reader vs. Preview, but I've been fine personally for several years without it on my Macs. So yes, you should be perfectly fine without it.
EDIT: One caveat that occurs to me...since you're using an emac, I presume you're running an old OS version and have an old version of Preview as well. I'm not sure if there are Adobe PDF compatibility issues with newer files using older versions of Preview. If so, that might be a reason to keep Adobe Reader around, but perhaps you should try using Preview as the default application if it's faster, and only use the Reader when necessary.