Depends a lot on the power source. I did use this technique in some races in my early Zwift days, without even knowing it was a bug or something that not everyone could/would do. I just thought that was the Zwift draft effect coming into play.
Then the Zwift Police told me that it was illegal, and I was not allowed to coast after making an effort to catch a group. Thankfully, this is allowed in the real world.
My Direto (V1) was "good" in this regard, as it kept the watts for quite a few seconds if coasting. The NEO2 however is faster in dropping the watts to zero, but my Assiomas DUOs is a bit slower than the NEO2, but still much faster than the Direto.
Now if only I could get rid of the drop outs from the Assiomas. Happened at least twice yesterday and cost me quite a few placings in the TdZ race as having your watts/RPMs at 0 for 5-10 seconds gets you dropped from the bunch pretty quickly!
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Luckily one of them was slightly downhill, so my avatar just coasted until it picked up the signal again...
Never (?) had these total drop outs with the NEO2 as power source, and will probably switch back to that again and then record the Assiomas output on the Garmin Edge instead...