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As far as chordal action goes,
It's the principle of the thing. It can be specced (not even redesigned, really) to be more efficient, so why not?
Like tester says, yuck. I want my cogs to approximate circles, not polygons.
A bigger reason to put more metal in your drivetrain is to reduce wear. It's certainly the main reason I hacked OSPWs into my RD-9070 cage; holds like 3% more chain. Bike weighs 6.14kg btw, so not gonna break the weight bank...
But the main reason small cogs blow chunks is the huge gaps between them, which get comically large below 12t in relation to what's actually desirable at high speed.
If you want to maximise your speed for a given effort, you need close ratios. Otherwise you're either going a bit slower than you could, or trying harder by spinning or stomping.
Kimmo-
Just put on a bigger chainring? (And use SRAM cassettes instead of Shimano, they have much more linear ratio gaps)
Your gears should be so that in a full gas flat sprint (1500W, 65kph) you are in the 13 or maybe the 12. The 11 or 10 is for descending at 70-80kph when you are are putting out much less power, aerodynamics is much more crucial and you are focusing on cornering and following the wheels.
No one can be bothered with half-step triples and shit in a race situation (TTs excepted perhaps)
leggy_blonde
Chordal efficiency worries only apply to racers where everything else is already optimised. The differences are tiny.