If you are storing things of an organic make up there is a possibility that it will succumb to degradation.  Things like clothing and fabric are hotbeds of activity for mold and mildew.  The last thing you want when reintroducing a  piece of furniture back into your home is musty smelling furniture full of mold spores.  Though our climate here in Utah is relatively dry there are many factors that can change the outside environment such as the temperature of the roof of your storage unit and fluctuations in temperature that can leave condensation.  Many have joked about our weather here  saying “If you don’t like the weather, just wait 10 minutes and it will change”!  The condensation that temperature fluctuations can be destructive in its own right, but that moisture also gives mold and decay the opportunity to flourish!