Hi lamont,
Compressing foams for longer periods of time can negatively impact performance. It would depend upon the material being compressed, the quality of that material, and the length of time it was compressed, amongst other things. Latex will tend to hold its shape longer than polyfoams by quite a bit. There are videos online from manufacturers showing latex that has been compressed for a few years and it still tends to rebound quite well, although Dunlop doesn’t seem to fare quite as well as Talalay.
Most simplified choice mattresses companies (most using some type of polyfoam) have a recommended time frame for compression of their products, often in the range of three-four weeks. The recommendations do vary by manufacturer, though. There is more information about the many factors that can impact the overall life of foam in post #2 here.
Phoenix