I can't speak for Matt, our sound guy, but here's what I know…
Many of the shots in the film involve steadicam/movement, and would have been very, very difficult to boom. And sometimes, it's just too hard to get the boom in a position that doesn't throw a shadow somewhere. I believe we boomed when we could, but it wasn't always possible.
It always seems like it's faster to lav, and, it just sounds cleaner or am I way off???
I listened to some audio from my feature and I sort of am not too crazy about the boom audio, but the lav audio is typically nice.
Matt should comment!