tree_reduce doc: explain benefit when building binary search tree

Author: rbruenig

src/lib.rs

@@ -2534,6 +2534,11 @@ pub trait Itertools: Iterator {
  /// arguments. For example if `f` combines arguments using `format!`, then `tree_reduce` will
  /// operate on average on shorter arguments resulting in less bytes being allocated overall.
  ///
+ /// Moreover, the output of `tree_reduce` is preferable to that of [`Iterator::reduce`] in
+ /// certain cases. For example, building a binary search tree using `tree_reduce` will result in
+ /// a balanced tree with height O(ln(n)), while [`Iterator::reduce`] will output a tree with
+ /// height O(n), essentially a linked list.
+ ///
  /// If 'f' does not benefit from such a reordering, like `u32::wrapping_add`, prefer the
  /// normal [`Iterator::reduce`] instead since it will most likely result in the generation of
  /// simpler code because the compiler is able to optimize it.