What you are doing at the resolution is more important than the size itself. If you're trying to play blurays or .mkvs most non-intel integrated GPUs should be enough. If you're web browsing or word processing it doesn't matter.
The reason is I have a 22” full HD external Asus monitor
, so I want to be able to plug the laptop into the big screen and work that way when at my desk. I also have wirless keyboard and mice. So, the laptop will basically sit on my desk with the lid closed.