In Breaking Away, this is true

Seriously though, smaller rings/cogs make for a lighter bike. Shimano even came out with a non-standard chain size (System 10), and the gears looked a bit freaky, like super fine versions of a full size cog. Track only, so no derailleurs etc. Nowadays compact drivetrains are popular.

On the other hand, smaller cogs are NOT as round, and there is a lot more friction. Shimano claimed to have a full time person working on making the most efficient 12T cog before they made a 12T. Think of it this way - a 2 tooth cog would resemble a line, and a 1 tooth cog a raindrop. Not very round. What this means is that it's more efficient to use larger rings/cogs, for both roundness and friction. To wit - the smaller drivetrain craze with BMX bikes just leads to more ring and cog sales, ditto compact road drivetrain stuff.

Larger cogs also make for smaller steps in gearing. For example, if you shift from a 22 to a 21, it's a really small jump (-1/22), so small that most cassettes (all?) don't have that jump. But go from a 12 to an 11 and that's a big jump (-1/12, or almost twice the jump as the 22-21). In the old days the TTT squads would use huge chainrings, partially to get bigger gears, partially so they could time trial much of the time in the meat of the cassette/freewheel, where the jumps were small (15 to 14, for example, instead of 13 to 12).

In a sprint I preferred using bigger rings, bigger cogs, to get a more gradual stepping up of gear, but at the top end it doesn't matter - the jump from a 12 to an 11 is big no matter what.

cdr