Now, i've seen alot of people calling the ''stage'' action group useless unless you can select stages. That isn't true, it can be used for a lot of things, such as on Mulbins Munbug (for example), there is 5 engines, there's an action group there wich toggles the gimballing of some of the engines to increase stability, however with the stage action group, you can turn the engines on, then release the launch clamps (needs to be pressed 2 times) and voila! Now it does it automatically. Another possible use of the action group is to toggle SSTO engine mode, it needs to be tooled a little with in the start, but after it's easy. Additionally you could replace the light action group for solar panels, if you have landers on a lander, you could change the ''gear'' action group to only deploy the main lander's landing legs, and there is so many possibilities out there for the use of these groups, but noone ever bothered to find out about them, so post your uses down below!