1. A blob is normally rather large (that's why it is called a large object). Normally every page (= 2 or 4 kb) has 28 bytes of overhead (header+trailer). A blob page only has 36 bytes of overhead. If you specify a blob page of 64kb for example their is only 36 bytes of overhead where normally is was (32*24). A lot more
2. The page size is also used for I/O. Reading blobs with biggers I/O's makes it faster to work with.
Due to changes in smart blobs their are a lot of advantgaes of working with the 'normal' small pages. So smart blob pages look like normal pages. However at creation time you can still specify the I/O size.