I like using constraints to encourage creativity. Canon is a pretty useful constraint in my opinion. If I can't make an idea work within canon I'll save that idea for a different campaign.

As a GM I have to allow some break from canon or else I spend too much time on research. The best example was my Westeros game. It took place after Game of Thrones, mostly during book 2. Everything from book 1 remained true to canon. After the players were inserted into the world I allowed things to change.