The stepper motors driving our printers move in "steps" of varying size. The majority of the steps are in between full steps. Full steps are the strongest magnetic positions. When the Z axis is positioned in between a full step it migrates to the full step that attracts it most, turning the lead screw and changing the layer height. Thus each Z layer height not set to a full step value while printing becomes smaller or larger than intended. Over multiple layers this will affect Z height accuracy. I used the RepRap calculator to find several favorable layer heights that will eliminate this problem. This is a PDF with the next higher and lower full step value of common layer heights for printers using common 5/16 ACME rod (which has .2728 pitch). the HIC Prusa uses these rods. If your printer uses these rods add a tag to this post. if your printer uses different rods create your own schedule and post it as well. Or ask me to include it.
For other size and pitch Z axis rods Here is a link to the calculator.
http://prusaprinters.org/calculator/