Very low moisture levels may cause problems with static electricity. Static electricity may cause print defects which will move around on the printed page and appear as streaks or "fish eyes". Proper storage of toner and a proper operating environment for the machine will keep many potential problems at bay.
On the flip side, humidity may cause it's own set of problems for laser printers and copiers too. Toner is hydroscopic it absorbs moisture very rapidly. The finer the toner particle is, the more susceptible it is to moisture absorption. It can begin to become a problem when the environment achieves a humidity level of 50% or above. The result can be print defects and/or light printing. For this reason toner needs to be stored in a cool dry storage space.
Happy printing!