A couple of years ago I brewed a 1.090 quadrupel that is truly excellent, but did not carb well at all, which is an understatement. Since then, when I brew a beer that strong, or when I have stored one in a secondary for longer than a few weeks, or when I have cold-crashed a beer, I will spend the extra $3 on some s-05 or champagne yeast to repitch at bottling. I have not have carbonation issues since -- perhaps this is completely independent of the extra yeast, but I think $3 is a pretty cheap insurance policy.