Lower receiver hole?

[jvencius]

What's the purpose of the hole at the top of the lower receiver that goes crosswise into the hole where the front takedown/pivot pin detent spring fits? Both of my lowers have it but apart from a lube point, I can't see any purpose to that hole being there and my simple little brain is confused...

[jvencius]

Here's a pic--the hole I'm referring to is just to the right of the pen tip:

[m24shooter]

To allow water to exit.

[Stickman]

Drain hole. Some people refer to it as a lube point, but the last thing I would want to do is drop any lube in there to gum things up.

[Eric]

And it's a feature some manufacturers omit. It's not exactly a critical item.
By the way, thanks for adding the picture.