Because Trump is unacceptable to most Republican voters, even though he's the frontrunner, this has enhanced the role of spoilers (i.e. Rubio, Cruz, Kasich). A spoiler can't win, but he can block a rival from winning.
Whether it's good or bad to be a spoiler depends on the specifics. The current GOP primaries raise some interesting questions about voter priorities and candidate priorities. Which is more important: opposing Trump or supporting a particular anti-Trump candidate? Preventing Trump from getting the nomination, or helping a particular anti-Trump candidate to get the nomination?
Is it more important to support a particular anti-Trump candidate at the risk of making it more likely that Trump will win the nomination–or opposing Trump at the risk of sacrificing your preferred candidate?
In addition, a campaign can be like a game of chess. You don't know ahead of time what's a winning move or losing move. You can't say in the abstract what's a winning move or losing move. That's because it depends on what the other player does. There is no winning move in the absolute sense, only in a relative sense.
As the campaign evolves, a winning strategy may become a losing strategy. Candidates must adapt to the state of play. And it depends on priorities. Each candidate wants to win. But in the event he can't win, who's the backup?
Take the Florida race. Cruz has a twofold agenda: defeat Trump and defeat Rubio. Those are his two main rivals. And he has an order in which he wants do to it: drive Rubio out of the race to make it a two-man races between Trump and Cruz.
That, however, makes Cruz a spoiler is a dicey sense: it's more important for him to prevent Rubio from winning than to prevent Trump from winning. Cruz has no realistic chance to win Florida, but he may be able to prevent Rubio from winning. That, however, means it's more important to his strategy to sacrifice Rubio to Trump. To make Rubio lose at the cost of Trump winning. Cruz's strategy requires him to become a temporary Trump-enabler, in the hopes of stopping him further down the line.
That's a very risky strategy. If Trump wins Florida, it accelerates his momentum. In addition, Florida is a big delegate cash cow. If Trump wins Florida, that makes it much easier for Trump to rack up the remaining delegates to win the nomination outright. If Trump wins Ohio in addition to Florida, then his nomination is probably inevitable.
Although it would be advantageous to Cruz to knock Rubio out of the race, it would also be advantageous to Cruz to deny Trump victories in Florida and Ohio.
That would give Cruz two possible paths to the nomination: winning the nomination outright, or winning at a brokered convention. If Trump loses Florida and Ohio, that's a backstop that probably keeps him from winning the nomination outright.
Cruz's preference is to win the nomination outright, and that makes sense. It would, however, be prudent for him to have a fallback.
Suppose Trump can't net the winning number, and Cruz comes in second. If at the end of the primary season, Trump is still failing to get a majority of Republican voters, and Cruz comes in second, Cruz would be the obvious alternative to Trump at a brokered convention.
For Cruz to compete in Florida is quite a gamble, because it runs the risk of a twofold loss: it may make it harder for him to win the nomination, and it makes it harder for another anti-Trump candidate to win the nomination. It clears a path for Trump to win the nomination. On that scenario, not only does Cruz lose, but the party is likely to lose in in November. And even if Trump wins the general election, that's just as bad in a different way. Trump winning or Trump losing to Hillary are both worse-case scenarios.