It's a little more complicated than winner-take-all or proportional representation.
Iowa is an old-fashioned traditional caucus state in which precinct delegates go to to the county conventions and then the state convention, which selects the actual state delegates.
The actual Republican National Convention delegates are elected by Iowa State Convention. In the real world, all but the winning candidate has usually dropped out by the time the national convention delegates get selected.
A serious threat of a brokered convention would change that dynamic completely and Iowa's delegates could be fought over bitterly at the state convention level since in a case like that every single delegate would count. However, we haven't had a brokered Republican convention since 1952 and haven't had a seriously contested race at the convention since 1976. Both of those are basically ancient history with little precedent-setting relevance to modern politics.
Interesting - thanks!
This is shaping up to be a truly bizzare primary.