@shahood said:
What's the purpose of favourite?
Hi,
I just wanted to know if there is any purpose attached to marking a title as favourite.
I mean, it seems redundant when a user can add titles to a custom list.named "favourites".

Widely used in the WEB interface by users who don't want to go through the hassle of creating a list.
Everyone has the 3 default lists.

• Favorites
• Watchlist
• Rating

Or does it contribute to any other statistics like popularity?

Yes, they are considered to calculate Popularity & Trending.
https://developer.themoviedb.org/docs/popularity-and-trending