One other thing to add, mostly about conventions and delegate voting, is that candidates can "release" their delegates to make them unbound prior to the first ballot. This is basically what candidates who drop out and endorse another candidate do. Those delegates technically don't have to vote for the endorsee (say if Christie had any delegates, they wouldn't have to vote for Trump just because Christie endorsed him, they would be unbound and free to vote for Cruz or whoever) but it's generally understood that they will. (And probably more because the conventions are near unanimous votes.)
In the old days when conventions mattered, often when a candidate peaked, but short of the necessary amount to win, he would release his delegates to hopefully screw over the other guy or two he was battling with. Hence, why so many conventions went to "dark horses" or compromise candidates.
Some candidates still don't release their delegates, simply to have their votes counted symbolically. Ron Paul in 2012 (along with a few unbounds who voted for Santorum, Bachmann, etc.), Kucinich in 2004.
Democrats were afraid Hillary wouldn't release hers before the 2008 Convention. Delegates were still voting for Hillary, so she called to suspend the roll call. Roughly a thousand out of the 4400 (gasp) did. And another 200 didn't vote.
Other than 1976 the only times delegates voted against the eventual nominee in significant numbers was every Democratic convention from 1980-1992. About a thousand Democratic delegates voted for Jerry Brown and Paul Tsongas over Bill Clinton. In 1988, Jesse Jackson had about 1200 (roughly 30%) who voted for him. In 1984, Hart and Jackson got about 1700 votes to Mondale's 2200. In 1980, Kennedy got 1200 to Carter's 2100. And ~700+ failed to show up for the VP re-nomination ballot of Mondale because they were upset that Kennedy lost. (Worth noting, Kennedy tried to get all the bound delegates unbound prior to the Presidential ballot...this was part of the impetus for the SuperDelegate system.)
1976 was the only real contested convention of the primary era as there were enough unbound delegates to decide the winner:
Ford - 1187
Reagan - 1070
Elliot Richardson - 1
