Easy… decoupling. You hit the pause button on your keyboard, it does not need to “know” (in code or compile time or at runtime) what your music player is, and it can still pause it. Similarly, you can write a new media player, and not have to convince 1000 different projects to support or implement your custom api. en.m.wikipedia.org/wiki/Enterprise_service_bus
It’s a clever torch stand. If it’s empty, you put your (long) torch in the top hole (stabilized by the bottom hole). If there is already one, you slide it two notches down instead and pivot the whole device (so it’s balanced). Same with the third, but pick/pivot out of plane with the others. Works with one hand, keeps houses from burning down, great widget.