What Is The Purpose Of The Small Pinhole Found In Many Locker Locks Next To The Key Hole?

The hole is there allow water and such to "drain" out of. If water gets into the lock and freezes without expansion room it could damage the lock or cause it to seize until it thaws.  Most padlocks don't use liquid lubricants as it allows for dirt and grime to stick, if anything it's graphite which almost everyone won't take the time to use.

Edit: Upon closer inspection it is specifically off centre to allow water to drain from the spring that actuates the shackle.

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