In all seriousness though, I can't see myself using it as anything other than the 'high' level settings in anything but the most plot-specific ways.
I tend to make a point of writing such rules anyway. As long as they're not a) entirely forgotten or b) actually getting in the way, it doesn't really hurt. As it is, some of my favourite special rules are fairly low-powered rules I originally threw on as afterthoughts.
Sgt Kronen, for example, has a rule that lets her halve visual penalties for darkness. I originally thought that this would be somewhat secondary to her various alacrity based skills as establishing her as a renowned tunnel fighter (she's from the Mordant 303rd "Acid Dogs", a night/subterranean world regiment active during the 13th Black Crusade*), but it really really isn't.
That she's got quick reactions may be more generally useful, but the fact she can fight in low light really sells the character.* Back in WD 284, there was a fluff article (by Andy Hoare and Graham McNeill, with some lovely illustrations from Paul Jeacock) about several of the regiments called up for the defence. It's the only time when I've actually
outright stolen so judiciously borrowed canon material for a character.