Huh? When I first set up my fixed gear the LBS put on a 1/8" cog and chain (had done other stuff myself, but when I buy things from them they put them on at no charge so what the heck?). Not realizing this a few months later I put on a new 3/32 chain which practically wedged onto the 1/8" cog. I could ride it, but with difficulty and noise. I suppose if you don't have any of those aggrevations it doesn't matter, but I could not have ridden on it. I put on a 3/32 cog so I could use "regular" chains.
FWIW,
Raymond