Fantastic Beasts and Where to Find Them is an expansion of the Harry Potter world, one that acts as a prequel to the book and film franchise we already know and mostly love, though we should talk about Chamber of Secrets at some point. More pragmatically, it's an opportunity for Warner Bros. to keep selling us movies based on J.K. Rowling's work now that the Potter books that served as the source material are done.
One of the key persistent components of the Fantastic Beasts marketing campaign has been its frequent intonation of this being "From J.K. Rowling's Wizarding World," an attempt to draw the connection between this movie and those that have come before it. Without any characters carrying over from the previous stories, there needed to be some brand continuity, and the "Wizarding World" phrasing not only brings connotations of the earlier movies but also ties in nicely with the Wizarding World of Harry Potter attraction at Universal Studios.
Franchise extensions like these and others are great ways for writers and directors to tell additional stories in universes they've already created. They're also a great way for studios to print some (presumably) easy money, even if the original stars are no longer available or interested in returning.
There are three key ways that modern movie spin-offs have been presented to the audience, with each one tackling the question of brand continuity and audience recognition a bit differently.