Multiple Speedlite EX question

Hi. I have another question in my never ending quest to master the Speedlite set up and implementation.

If I set a 550 or 580 as "Master" and a 430 as "slave" and do nothing more, what, if anything, is the resultant flash output or result? Do they both trigger as if individually for the same exposure, or do they work in tandem to properly expose the scene? I ask, as it seems easier in the end to set them up this way and simply dial in some negative fec for the fill flash when doing, say, a portrait, and then not having to mess with the ratios and groups.

Thanks.

By default I believe they will work in tandem to properly expose the scene. Without ratios you'll get a flat look, the idea of multiple lights is to add depth and shadows. You can only have two groups on the subject, group C is for backlight only.