First, the old adage 'Keep your friends close, but your enemies closer' has a lot of truth to it.
Second, I think BYU would have greater success in the Big 12 than utah will have in the pac12 which would definitely hurt recruiting with BYU going to more and better bowl games annually whereas BYU's success in the pac12 probably wouldn't be as great a difference.
Third, BYU's recruiting would be enhanced because we already have large LDS numbers in the West, but having conference affiliation in the Midwest (especially Texas) would help our recruiting there.
Just my opinion though.