The first process involves reprinting the content of an old title and giving the book a new cover. Some minor elements maybe adjusted to allow the title a fresh new look and feel but for the most part, the content remains the same.
The second process involves consolidation of several books into one (albethey somewhat lighter versions of their standalone counterparts.) This product is commonly referred to as a 'Compendium'.
Wizidification allows the publisher to essentially charge their customers multiple times for the same book or books.