I didn't know this until recently, but windows require weep hole vents too.
My neighbor had PVC (polyvinyl chloride) windows installed last month. A few days after the installation, it rained and condensation formed on all of his windows. But this wasn't the kind you could wipe away.
Apparently, PVC windows have multiple layers of glass for insulation purposes. And since they forgot to make make weep holes between the layers, the water got into the middle layer and caused condensation. Three days passed without rain and my neighbor still couldn't see through his windows!
He complained to the manufacturer and had all of his windows replaced. Weep hole vents seem like such a small detail, but they're important. Having witnessed what my neighbor went through, I've definitely learned that.