For instance, an everpresent threat in Starcraft is the Zerg Rush, in which a player skips building an economy to build zerglings---cheap, light, raider units--- to attack the opponent early before he has any defenses (as he, presumably, has not skipped building an economy). The zerglings are melee attackers, so holding a small choke point is an effective way of only allowing one or two zerglings to attack at a time, even if there are more (usually 6-8).
Of course, this poses a problem---if the tight spaces allow only two zerglings to attack, that's great, but the tight spaces also only allow two of your workers to fight back. Actual fighting units will slaughter worker units, so you've merely slowed your death, not prevented it.
Except! By ordering all your workers to harvest the same mineral patch, you can activate this collisionless behavior described in the article, and then fit your "super-group" of ten or so workers into small spaces---to fight the two zerglings at a time. The workers can definitely win now!
This has become a giant wall of text, but this is actually basic, easy, essential knowledge for the competitive starcraft 2 player, so it's fun to see its origins in this article.