There's a lot of chatter on SOS and "who to root for" each week (e.g. "it helps us if TTUN beats ND, or "Wisconsin sure didn't help us by losing to Illinois"), but ultimately, SOS has yet to really factor into the CFP picture and the playoff formula has been simple for P5 teams:
1. Run the table as a P5 team and you are in. 100% of the time. (6 of the 20 CFP participants to date have run the table).
2. If you lose once, win the CCG. 92% of the time this results in a CFP entry (12 of the 20 CFP participants to date were 1-loss CCG champions). The lone exception was last year's Buckeyes who had 3 undefeated teams ahead of them and another 1-loss CCG winner who avenged their season's only loss.
18 of the 20 CFP participants fall into one of those top 2 scenarios and 18 of the 19 P5 teams to meet those criteria have made the CFP.
3. If you lose once and fail to win a CCG, hope and pray that only 3 other P5 teams finish with 1 or fewer losses. 7 teams have been in this scenario with only 2 making the CFP: 2016 OSU and 2017 Bama. TCU and Baylor missed out in 2014, Iowa and Ohio State missed out in 2015, and Wisconsin missed out in 2017.
Teams that have lost 2 games have made the CFP 0% of the time. At some point (think back to 2007) it is bound to happen, but it is not going to be a path often treaded.
There's so much chatter about strength of schedule but it has never really come into play. Ultimately the CFP is based on the same principal college football success has always been based on...DON'T LOSE. And if you do, definitely don't lose twice. 2017 Bama proved that SOS can mean nil. Their best OOC opponent finished 7-6. Their best wins came against two 4-loss teams that finished 18th and 19th. Even their loss came to an eventual 4-loss team. This year, Clemson may be asking the 2017 Tide to hold the Tigers' beer as their anticipated toughest conference opponent is now 3-4 with wins over Liberty, W. Michigan, and Holy Cross, and their anticipated toughest OOC opponent has yet to win back-to-back games.
So who cares if ND beats TTUN. And who cares that Wisconsin lost to Illinois. Just win baby!