u/Fun-Efficiency-2958

Currently doing some welding on the car and I dont know what this hole is for. Initially I thought that I would weld it shut, but it looks like it's from the factory so I'm not sure. The car had problem with water getting in the cabin, the foam under the carpet was completely soaked on the passenger side (where this whole is) and a bit on the driver side. I thought that this hole is one of the reasons why.

Saw one video where the guy was welding it shut. So should I do the same or?