What this means is that if you wanted to mark the outline of a rectangle, for example, the corners would be very dark compared to the rest, because as the laser head slows for the corner, the power must be reduced correspondingly. All DSP controllers do this, as do GRBL and Smoothieware.
Even shapes that don’t have corners have points at which the laser starts and stops, and you’ll get black marks there as well if power ramping isn’t managed by the controller.