Is there any speed difference (i.e., less popcorn effect) between actions that grouped a bunch of devices together versus individually listing them in a rule?
The log below shows a group of devices (bottom line- App:360) versus individual (app:86) actions listed on separate lines in the log.
I haven't tested using stopwatch or anything, but I find that using groups for lights I'm turning on/off has been more reliable and seems to reduce popcorn effect. I switched a night-time "lights out" automation from individual to a group and the first time I ran it that way I was surprised how much better/smoothly it ran.
Related but separate info - HE staff has said that groups have less overhead than scenes, so if you don't need the additional fine control of a scene using groups will be more efficient.