They definitely matter. In addition to things like font size and capitalization, the physical size and shape of a book can also be an issue, unconventionally shaped books can really fuck up a nice shelving system! Although I find this is usually more an issue with large art and photography books than fiction or non-fiction.

Back in the 90's there was a magazine called Raygun that used to be "playful" with their type and you'd constantly see shit like one small word being s t r e t c h e d out across a line, it was super irritating.