Hi Ray,
I have been mulching with black plastic for a few months now to weaken rampant horsetail and bindweed on my plot. These particular weeds are so strong and persistent (particularly horsetail) that they will make a bee line for any daylight at all. So, if you are mulching to knock back weeds, depending on which ones you are dealing with, punching holes in your mulch sheeting may counteract the very thing that you are trying to do.
If your motivations are otherwise, ignore what I have said! Good luck!