Yep... trying to fit so much story into an ideal number of pages. For example, in the past week I've been reading two mass market paperbacks with vastly different font size. One is Robert B Parker's "Shrink Rap", which is about 300 pages with huge font and margins. The other is John Irving's "Prayer for Owen Meany", which is over 600 pages with tiny font and thin margins.
Sometimes larger font size can help make a book feel like a page-turner. I'd probably feel ripped off if I bought Shrink Rap, but seeing as how it was from the library, I was quite happy to finish the book in a day. Owen Meany, on the other hand, sometimes turns me off with its bulk. I can spend an hour reading and only get a couple pages ahead. It makes me more likely to put the book down if I see that I'm still less than 10% of the way through it after nipping at it for a month.
Speaking of which... I'm very glad I had a chance to thumb through the pages of Elmore Leonard's book of writing tips, rather than ordering it from Amazon. The font size is huge, the margins and blank pages take up more space than the text, and the whole $20 book might run 5,000 words. Don't write the parts that readers usually skip. There you go. That's pretty much the book in a nutshell.