There are, and they are. The trainer, in general, is unforgiving, and rewards steady state power. That's more of an indoor cycling thing than a Zwift thing. When I was training, I derated my indoor power targets by 7%, but 10% felt more like it (I still had 7% targets, damn coach
) Add the draft effect in Zwift and you get penalized for slacking off a lot more than you would on the road. It makes for great training, though.