Dust and moisture are the enemies of your equipment's longevity. I'm sure most of us have experienced the annoyance of a foggy lens when moving from one environment to the next, but what about when that fog turns to fungus? Every lens eventually gets some dust in it, even the wonderfully expensive weather sealed professional lines.
By itself that minor amount of dust isn't really a major issue, but once moisture enters the equation the result can be devastating to your gear potentially leaving permanent etchings on your once beautiful glass. The usual preventative solution is to cram a bunch of silica packs into your camera bag to try to control the moisture... BRNO has a better solution.
Rather than keeping a bunch of loose silica packets in your bag (which almost always tear open) check out BRNO's Dri+Cap System for Nikon and Canon. It's a set of specially designed body and lens caps that are built to carry silica-gel packs. They also feature a rubber o-ring seal to keep outside air from entering the lens through the mounting area. This system allows your gear to stay at the proper humidity as well as more easily transition between varying temperatures or environments with far less to worry about.
Coming in at $45 for a set (body and lens cap) it's definitely an option worth considering.