User blog comment:Paamanking/Garen's Passive during a Clash/@comment-4080931-20130104053802

Well yeah, it does nothing in a teamfight. Which is sort of the point, Garen's passive sacrifices teamfight capabilities in order to excel at health regeneration during roaming and laning. Why would you need to change this?

Note that having that regen outside of teamfights may also boost him in teamfights indirectly. For instance, he can dominate someone in lane and render him useless for a long time, while getting fed himself which results in teamfights where that enemy is piss poor and Garen is able to do some more damage and survive for longer.