controlling 6 stepper motors from PC using arduino mega

If your code does what you want it is fine.

I am just trying to draw your attention to the difference between .A. causing a "wait" period using the delay() function (which paralyses the Arduino until the delay period finishes) and .B. causing the "wait" by using the Blink Without Delay technique which allows the Arduino to do other stuff while working through the "wait" period.

...R