I've never known this setting existed until sometime within the last 10 years. As a kid when you go through the settings option, it's not intuitive what Set means or what Shift means or how it will affect what setting. I've always used the default option in games, whichever it was, Shift? The one where you're allowed to switch in a Pokemon before the opponent sends out another. I've never seen a reason to change the default setting. Handicapping yourself? Basically I'm a default setting person.