The first is obvious since he's the starting quarterback. Take the starting quarterback away from any team and there would be struggles.
But there are more subtle ways he will be missed offensively.
Romo's experience allowed him to not only get the Cowboys out of a bad play and into a better play, but into the right play. Sometimes the formula quarterbacks follow from a game plan can avoid negative plays in those situations, but Romo often could turn those into big plays.
The running game will be affected by Romo's absence. As much of a weapon that Dez Bryant is, not having Romo on the field hurts the passing game. Defenses would be more inclined to stay away from eight-man boxes. With Dak Prescott, defenses will challenge him to make throws early on even with his preseason success. Defenses will look to stop Ezekiel Elliott.
No matter how good the offensive line is -- and it has played like the best in the NFL in the preseason -- it cannot account for an eight defender.
The Cowboys will miss Romo defensively, too. A lot.
No, Romo can't rush the passer and he can't take the ball away, but he can impact how much or how little the defense plays.
The formula the Cowboys followed in 2014 is one they hope to follow in 2016. Losing Romo doesn't change that necessarily, but it does make it more difficult.
The misconception is that the Cowboys just played keep-away from other teams with DeMarco Murray running left, right and up the middle. Murray did run left, right and up the middle, but the Cowboys also scored a ton of points. That meant more than any time of possession advantages. With leads, the Cowboys forced their opponents to play catch-up and made them one dimensional.
Even with a limited pass rush -- remember, Jeremy Mincey led the Cowboys with six sacks in 2014 -- the Cowboys finished 12-4. If you're looking for a big reason why the Cowboys went from 31 takeaways in 2014 to eight in 2015, the offense's ability to jump ahead is one.
So as the Cowboys get ready for life without Romo for however long, their defense will have to perform better than expected, unless you expect Prescott to play at the same high level that he has shown in the preseason.
How does life without Romo affect the defense?
It depends on whom you ask, even in the secondary.
"I don't want to say it's extra pressure on us, but it is," cornerback Morris Claiborne said. "Without your starting quarterback, you have to get off the field, you have to get turnovers and get three-and-outs and get off the field. And you have to help the offense by scoring points."
Fellow cornerback Brandon Carr disagreed.
"I don't think it really puts the pressure on ourselves as far as doing more," Carr said. "Before this season started, we had our mindset that we've got to do more, period. What we did last year wasn't acceptable and it wasn't our style of football. We're harping on it and just leading by example and trying to create good habits early and often."
Ten days before the regular season opens against the New York Giants, the Cowboys aren't sure who will start at defensive end and what their defensive line rotation will look like. Maybe it's Benson Mayowa and Jack Crawford. Maybe it's Mayowa and David Irving. They will not see fourth-round pick Charles Tapper play a preseason snap.
The Cowboys have five sacks in three preseason games, and two of those sacks came from Shaneil Jenkins, who was waived/injured on Monday. At linebacker, Sean Lee is working through soreness in his left knee, which required arthroscopic surgery in the offseason. The projected starting secondary has not had an interception in the preseason and its members did not have one last season.
At times this summer, the Cowboys' defense looked better than expected, but some of that is based on low expectations.
Without Romo, the defensive questions seem more pronounced.