Thx for explaining the benefit of variance, this probably puts to bed an idea I had where miners wait 9 minutes after the last block (ignore for the moment that there's no universal time in bitcoin + dishonest miners) and then turn their miners on (this would make mining less costly).
 
What you're saying is that this scheme would have the effective variance of 1-minute blocks and thus be undesirable?
If anyone has a link to some 'non-napkin' graphs on this thanks in advance!