Not into it personally. Shorter radii of smaller rings and cogs increases drivetrain friction. Fewer teeth carrying the same load means they wear out faster. I run as large a ring as I'm comfortable with, in the case of my 29er that's a 36t ring plus a 24t cog.
But then I don't grind. Log-overs and occasional rock crawling is as bad as it gets for me.
Plus I imagine my rides are quite a few miles longer than the average BMXers'.