this desiccant functions sort of like a sponge. if you put a sponge in a bucket of water, pull it out and squeeze it, there's less water in the bucket and the sponge is ready to accept more water. plugging this thing in is squeezing the sponge. if you put a sponge in the bucket and squeeze it, the water doesn't go anywhere, same with leaving this plugged in. if you want a continuous system to leave plugged in constantly, look at a dedicated dehumidifier or a golden rod.
This unit should not remain plugged in longer than the suggested re-charge time of 8-12 hours.