As part of a homework assignment covering implementation of introsort I'm asked why heapsort is used rather than mergesort (or other $O(n\log(n))$ algorithms for that matter).
Introsort is a hybrid sorting algorithm that provides both fast average performance and (asymptotically) optimal worst-case performance. It begins with quicksort and switches to heapsort when the recursion depth exceeds a level based on (the logarithm of) the number of elements being sorted. (Wikipedia, retrieved 2014-May-06.)
The only reason I can think of is that heapsort is "in place" ... But tbh I don't really understand why this would matter here though.