Movie tie-in books

Origial Book Cover
(Source: Barnes and Noble)

When I visited a local bookshop to buy a copy of the book 'Life of Pi', I was told by the gentleman at the counter that the book was out of stock and only the movie tie-in version of the book is available, when I visited another bookshop to buy the same book they had the same story to tell me.




Movie Tie-in Book Cover
(Source: Barnes and Noble)

What exactly is a Movie Tie in book ?
A book based on a media franchise e.g: A Movie, television Series, Comic Strip etc.

What exactly is the difference?
Nothing that I noticed, except the cover of the book that may feature the actors or characters in the franchise.

Should I buy them ?
As an adult you should be able to decide what you should buy and what you should not buy.

I am not an adult can you please advice
All Right then!!, I don't see anything special in a book which features a movie star unless I am a fan of that movie or the actor, but as a avid fan of reading I see value in the text rather than its promotional material.