Options are confusing. Who can and cannot be sent to the minors isn't always public knowledge, so it's hard to keep track of it all. Luckily LoHud breaks it down for us. Only players with options and players that have contracts that allow for minor league reassignment can be sent down. Otherwise the player has to go through waivers, where other teams have a chance to claim them for their own.
The Yankees on the 40-man roster that can be sent down are Dellin Betances, David Phelps, Adam Warren, Austin Romine, David Adams, Corban Joseph, Zoilo Almonte, and Melky Mesa. Most of those guys have spent very limited time in the major leagues, if at all, so that's more obvious. The players with the most question marks are Francisco Cervelli, Eduardo Nunez, Cody Eppley, and Ivan Nova, who all have one option remaining. Chris Stewart and Clay Rapada are out of options.
Sometimes players that sign minor league contracts have options as well. Matt Diaz and Juan Rivera are able to opt out of their contracts if they don't make the team out of Spring Training, and only one of them is likely to. That means instead of being reassigned to Triple-A their contract will be terminated, and they become free agents. Dan Johnson has a similar situation, but he can be sent to Triple-A until a specific date where he'll be able to opt out. Jayson Nix, and relievers Jim Miller and Josh Spence can be optioned down.
These factors play into how the Yankees put together their Opening Day lineup and how they'll keep it as the season goes on. The people with options have a less immediate need to make the roster; if they don't, they can simply return to Triple-A. Players like Diaz and Rivera will get an extra long look and every chance will be given to them in order to make the team because otherwise the Yankees can lose them.
Rapada and Stewart will almost certainly make the team due to their lack of options and the way the Yankees have managed their roster in the past. The organization does not like to give up their depth, and it usually does not like to actually use it. Think back to the time Russell Martin was hurt for a week, yet no new catcher was called up.
If the catching battle ends up being Cervelli vs. Stewart for one roster spot, Chris Stewart will get the nod and Cervelli will be forced to sit in Scranton. Regardless of how it ends up, Stewart will be on the roster, whether as a backup or a starter.
Clay Rapada will be on the team as well given Girardi's love for using lefties, and his desire to have a second lefty in the pen. Cody Eppley and the newly acquired Shawn Kelley might challenge Rapada, but at the end of the day, they can be saved for another time. Nunez and Nix can both be sent down in favor of the other, depending on who impresses more, and Nova could be booted out of the rotation and maybe even the bullpen if they think he needs to work on his game as a starter.
These options might sound insignificant to fans, but they are very important when considering the shaping of the Opening Day roster and beyond. When you wonder why Chris Stewart is still on the team in a few months, remember why.