I love books you read straight through from cover to cover but I also adore those where you dip into them as and when.
Things like the Guinness Book of Records come into that category. I'm currently reading a "big book of facts" produced by Classic FM but will almost certainly have regular dips into this, rather than read it straight though. (To be fair it is a HUGE book).
I also like the way this mixes up my reading a bit as I read flash fiction (as well as write it), short stories, and novels. I also dip read. Dip reading is also useful when I've finished a book and am not quite sure what I'm going to read next.
I often fancy a change of mood after completing a novel and until I know what is next on my reading "menu", I will dip into books like this until such time as I do know.