Someone told me that having the pf repeatedly cool and heat can cause them to warp.
cannonfodder wrote:The only issue you will have is if you tighten your portafilter into the group as if you were pulling a shot. That can cause premature wear on the group gasket from the compression. Beyond that, the large thermal mass of the portafilter will help regulate the group head temperature. Locking in a cold/room temperature portafilter will also cause your group head temperature, even with a large E61 or saturated group, to drop like a rock. I have seen them go down almost 10 degrees simply putting in a cold portafilter.