I want to talk for a bit about something I sometimes see in RPGs (and, less often, in other games): mechanics that resolve one thing while producing a side-effect for something else. For example, critical hits in D&D, divine interventions in In Nomine, and the complications/opportunities system in the Leverage RPG. For the purposes of this article, a side-effect mechanic is primarily about one thing (whether you succeed at something, generally) but that produces a side-effect that is taken into consideration elsewhere in the game.
First, though, I’m not a huge fan of side-effect mechanics. I find they usually add more complexity than benefit. They can be jarring if the side-effect is something fairly removed from the original thing being resolved. Side effects have to be balanced such that they work with the core mechanic, neither ruining its original feel nor making the secondary effect insignificant. In short, the whole concept is troubled from a design perspective. Still, there are times when it’s completely appropriate. Where and when is the key question.