Current RC proposes removing min_samples_leaf. In my experience across numerous projects and competitions, this param is very useful for generalization. Conceptually, I've often seen extreme outliers like this (top left point) result in picking a single point in a group leaf, which clearly isn't what you want. Larger leaves have less variance and therefore generalize better.

This param is also one way to reduce tree size:

@amueller requested adding this issue in this twitter thread https://twitter.com/jeremyphoward/status/1036110165236363266