I have never tested the theory, however, I have been told by an instructor that if you do place a moisture barrier in a crawl, to do it gradually.
for instance;
That damp crawl space is keeping the flooring and all components attached to it at a certain "moisture level"
Once you apply a barrier, you are eliminating the source of moisture that is keeping that cellular material at its current "swolen" condition (for lack of a better term).
That cellular material now begins to shrink and, if the shrinkage is rapid enough, cracks will begin to appear.
His recommendation was to leave an area about 3' wide at the perimeter uncovered, and slowly, over a period of weeks or months, move the barrier towards the foundation until it covers all the ground.
I guess the theory was that if done slowly enough the structure will acclimate and minimal damage will occur.
Personally, I dont understand how eliminating moisture gradually will minimize shrinkage. Shrinkage is shrinkage, gradual or otherwise.

Anyone ever had a shrinkage problem? other than Seinfeld's Costanza?