Caulking trim before you paint it is one of those semi-boring jobs, but I can guarantee you that caulking the holes and cracks in your trim before you paint your walls will make a HUGE difference in the finished look of your paint job! Filling in the seams between your baseboard, casing and walls, and filling nail holes will make your finished, painted room look so smooth and professional. Here are some caulking tricks that I've learned over the years as I've painted many rooms in our home and others.
We're currently working on Little B's room makeover, and her trim hasn't ever been caulked properly. I've been fixing that this week, by going over all of the baseboards and window casings in the room with my caulk gun before we paint.
When it comes to trim work like board & batten (like we did in our powder room), caulking is of utmost importance to give the trim a nice, finished look.