Just used DNA Painter for the first time. Astonishing. With new genealogically-known cousins popping up every few weeks on my lists at 23andMe and MyHeritage, I can now localize DNA segments to 1 grandparents, 4 great-grandparents, one (non-overlapping) great-great-grandparent, and one (overlapping) great-great-great-great-grandparent — for a grand total of 14% of all possible segments securely identified with an ancestor (if I chose to be looser about it, the % would approach 20).
This awesome free utility makes it possible to visualize them all in one chromosome map, which you can compare against matches of unknown provenance. Something I never thought possible.