If you're only running one program, you're probably right. But once you're running multiple apps, at least in my experiments, it seems it is less taxing on the system to use a hosting app. Originally I thought that (for example) running two apps (say, SWAM and Model D, each set to respond on different MIDI channels) would be more efficient than running three... i.e. those same two apps plus a hosting environment (so using the host would be something you'd choose for some other benefit). But while it may very with the app combination, from what I've seen, you actually seem to gain some efficiency (or predictability/stability) by running them via the host, as some elements of the individual apps are no longer being used.