I have some vision problems (I'm old). Reading an eBook on my Kindle is so much easier on my eyes than reading a pbook -- I can go for hours. It's one-handed operation lets you read anywhere, sitting, standing, or lying down, unlike a pBook which pretty much demands both hands, a good lamp, and a chair, at least for me. If your pBook has glossy pages, you have to hold it carefully so it doesn't catch the glare from a lamp Those are the two big issues for me.
I read technical books and manuals using Kindle for PC (also from Amazon, free). Sometimes I convert other file formats (like pdf) to Kindle format for this purpose. It is so much easier to search, highlight, bookmark, and take notes in an eBook than a pBook.