lsfire ... this SHOULD clear up any and all confusion ...
The cello is not, as others have said, impermeable ... it's a porous material ... although it DOES serve to deter moisture from leaving, it's principal function is to protect the wrapper from being damaged ... that said, it can also damage the wrappers of non-celloed cigars in your humi, so it's generally better to store celloed cigars and unclelloed cigar seperately to the extent possible ...
I used to be a BIG believer in cello off, but have come to the realization that in terms of maintenance, cello-on or cello-off makes no real difference ... so, I now leave it on because it's less work and as mentioned, it DOES protect the wrappers of the cigars it's on ...