All the members who thought otherwise, don't worry. I am sure the OP intended the title to be deceptive.
Sure size matters on both accounts! haha But, seriously I think the size of a page does matter if you want people to stay on your site for any length of time and I assume you do! If it takes a visitor 30 seconds to read the whole page, then they're not going to hang around there long. I think you should have informative, fun or interesting text that makes someone want to be on your site. Think about it, if you have ads and are trying to make money, do you want someone to spend less than half a minute on your site?? The longer they visit, the more likely they are to see something that interests them and click! click! click!
Well, if the page is extra short, you just say, "hmm nothing much found here" and you go to next site, but if it is very very very long you might say "oh damn, i dont have time nor mood to read that much text" so maybe something between it, which is not too short also not too long but have the knowledge you are looking for.