Embroidery backing come in two types, cut-a-way and tear-a-wear.
Use tear-a-way backings on jackets, caps and bags.
Cut-a-way backings should be used on most other garments sewn.
One layer of mid-weight backing is all that should be used in the ordinary sewing process. Use of multiple layers of backing (except in the case of poly-mesh below) is an attempt to maintain registration in a poorly digitizied design. Have the design corrected. When you use multiple layers of backing you are really quilting instead of embroidering and will most likely cause more puckering and distortion of the design.
To avoid that block of backing that often shows through light colored garments use one layer of poly-mesh type backing with a layer of tear-away behind it for additional stablization during the sewing process. After sewing tear off the excess tear-a-way and trim the poly-mesh around the design. This combination of products is also useful when embroidering on t-shirts and sweatshirts.
Applique sissors are just the right size for trimming backing and will help you avoid nicking the garment when cutting the backing.
When trimming backing hold the corner of the backing up, so that the garment is falling towards you. Slide the sissors around the design rather than opening and closing the sissors in a cutting motion. You will be less likely to snip the garment.
