When using rotary on a desktop fiber laser engraver, it usually marks an area, then rotates, then marks the next area. You will notice the gap between every two sections. It is caused by the non flat surface of work piece. We do not see the gaps on regular CO2 laser machine because it marks line by line instead of area. Gaps exist between every two lines so they "even out" and do not stand out much.
Although we can compensate the gap in the laser software, there is one more problem. When marking area by area, if the rotary is not placed in parallel to the x/y axis, the edges will not be smooth. Same issue exists when the part is not perfectly round or the rotary is not super precise. Here is an exaggerated result of a rectangle.
We could set each area narrow to make it like a line. Doing so will give us a closer result to the CO2 laser machine's.