In the last several years I've seen larger format books alongside the familiar pocket paperbacks. Sometimes these are taller, sometimes they are wider, and sometimes both. I've wound up with these in some cases due to them being given to me as a gift, or they were available while 'normal' sizes weren't. While I've observed the larger books being a bit easier to hold while reading, I haven't observed improvements in readability. A downside of the larger sizes is that they don't fit as neatly into my novel collection which is mostly of the pocket paperback size, and they are slightly less portable too - no longer pocket size.
While the benefit of larger size and print may be a subjective matter at the personal level, has there been reporting on widespread benefits of large format books?