It's always fun to see someone quoting me, so lets discuss...
in cata DOT clipping isnt a loss like u said, it's a benefit, if u put a refresh a dot before the last tick it will make both of the dots do all of their potential damage(in a way that no tics will be wasted)...
Soo as u took flame shock i will talk about it, lets say it lasts 20 secs ticks every 2 secs, that means if i refresh it at 19th second of its duration the new dot will last 21 second but will have an extra tick, soo by refreshing early you can have 100% uptime on dots.
However, here some dots have their tick timers refreshed once u reaply them, meaning in theory if u would spam shadow word pain, you would do no damage. Potentially making dot clipping impossible due to dots refreshing themselves all the time(meaning letting them fall off gives possibly better results than refreshing before last tick which would be wasted.) now i dont want to be one sided here, i think warmane did some fixes here and there my info might be quite old and no i didn't bother to test it, i will leave it to you, but that's what people were talking.
Before you ask i was talking about warmane doing some fixes about haste increase on channelled(aaand some other) spells. But i believe they might have done something about clipping(atleast sort of) too, not sure needs a test msg 2 long wall of text af