ESPECIALLY where you will be hanging TV's, closet shelves, bathroom rods, toilet paper holders and anywhere you run speaker or other wires, etc. If you know where you'll be hanging things - backer boards in the wall are awesome. I always like a towel rod, curtain rod, TP holder, etc. to screw into wood, rather than in drywall with an anchor.
2013 X-25 - Love it!
2007 X-15 - Sadly no longer mine