Cruz can do a lot of damage to the Scott Walkers and Jeb Bushes of the GOP during the primaries. He's very popular with the base, where Walker is middling, and Bush is unpopular. Cruz isn't likely to make it through the primary, but he's a bulldog, smart, and totally ruthless. Only Rand Paul will occupy *some* positions to the right of Cruz, in all likelihood, so he'll have a conservative ideological edge over most of the field.
None of these guys can win a general election after going through the far right circus that is the Republican primary, of course. That's why I'm surprised to see legitimate candidates like Cruz, Walker, and Bush preparing their campaigns. Cruz is young enough to wait out 8 years of Hillary. Paul Ryan has made that choice, and I think it's the right one. I question how palatable social conservatism will be in 8 years, when the country is already center-left on social issues, but I guess we'll see.
And this is why a two-party system is literally insane.
The primary is going to end up killing off most of the popular candidates (if you actually like someone like Ted Cruz, I mean) and will drag the eventual winner deep into the "Do as we say and remember that we know where your wife and kids are" territory of the power-obsessed oligarchs.
It's not even unheard of for Democrats to actively promote people like Ted Cruz exactly because a.) his candidacy will weaken others' and b.) he's unlikely to win the general election. That's some wonderful and sensible politics right there: rather than field a candidate and platform that makes sense, just *** over the competition so that no one is happy.