Why did they add the burrow scene in Harry Potter and the Half-Blood Prince?

David Yates (HP6 director) said they had to remove some of the most important details from the sixth book, like what the other horcruxes are and like the fact that they know that the deathly hallows are impotant and so delibretly showed them less, like only showing the invisibility cloak only once in the film - but still somehow had time to add a scene which didnt make sense and messes up the story for the last two films (the wedding by the burrow). How does this make sense???