Pasha,
This isn't exactly what hardstyle laziness means. It doesn't mean holding back as much as being efficient. It means undertanding the difference between power and effort.
Maximum power is achieved with the right effort, at the right time, for the right time. Excessive tension at the wrong time(s) robs power; it just slows you down.
Hardstyle laziness means being able to generate the right amount of tension when you need it, and then immediately relax when you don't. But it doesn't mean deliberately holding back on power.
When doing a longer continuous set, it IS appropriate to dial back the power somewhat, but the same efficient pattern of power application should apply to each rep.
Hope this helps.