G-1000 is a tough material and the tight weave (except G-1000 Air) makes it naturally pretty wind resistant. But by adding Greenland Wax (made from a mixture of beeswax and paraffin) you can increase this wind resistance, make the fabric even more durable and add water resistance. By removing it, you can make it lighter and airier. All you have to do is wash your garment two or three times.
Note that Greenland Wax offers water-resistance, not waterproofness!
Some products are made from a combination of materials, G-1000 and synthetic stretch fabric for instance. It is only G-1000 that can be waxed! Take extra care when waxing these types of garments to avoid getting wax on non-G-1000 materials.