I have to say that I beg to differ.

Now then, I've never actually seen a reed at full chat under a high speed camera, but given that it is primarily a one way valve then it would need to completely seal the crankcase for it to be effective. Look at the blowback on an old piston ported or a rotary valved stroker that's been tuned for more power and you can plainly see that having the case unsealed at the wrong time is not good.

Yes an engine will probably run without the reeds installed, but not particularly efficiently.

Let's say you have a transfer port effective area of 850mm^2, and a 32mm carb (804mm^2) then during crank case compression you'd lose a lot of the charge back through the carb, but maybe transfer enough to keep it running. That's not taking any intake velocity, or exhaust suction pulses into account.

From various literature written by people who know more than me, a reed valve opens around 120 degree BTDC at low rpm, closing again at about 40 degree ATDC. And then there's a pretty linear change up to high rpm where the open duration increases from 160 degree up to over 200 degree, but the opening point has now moved to about 80 degree BTDC while the closing is some 120 degree ATDC. So basically the reed valve 'adjusts' to the engine requirements.

A simple 2 stroke engine is only an air pump after all. Try taking the reed valves out of your air compressor and see how long it takes to get any pressure.