you are, at the very least, losing some very good and entertaining football and basketball games that will likely be filled with teams that aren't as competitive. I have noticed a lot of fans brushing off attendance from BYU fans at road games as not mattering, but the Pac has a Pac problem of a lot of empty stadiums in the conference, and BYU is the best team in the west to help fill those empty seats. I guess you could look at it as BYU making those teams look silly by having more fans at the games than the home team, I dunno.
Honestly, BYU has always been a no-brainer for the Pac12, but they just have never been able to get over the religious aspects, so the Big12 is honestly a much better fit for us, and I think a major miss for the Pac. I guess we'll see how the conferences match up in terms of success over the next decade, but I wouldn't be surprised at all to see the Pac continue to struggle to get traction in the CFP rankings compared to the Big12.