Well, if you take your lens out and take it into daylight, you're actually killing the fungus spores. I know a photog who specializes in landscape photography. He has never owned a dry cabinet, and his lenses are over 10 years old and no fungus ever, becasue he's out in the sun a lot.
If, on the other hand, you keep your lenses indoors for long periods od time, a dry cabinet is a must in SG.