How did commeātus semantically shift from meaning "passage" to "leave of absence"?

[scherz0]

What semantic notions underlie meaning 1 ("The act of coming and going") with 5 ("Leave of absence)? Please fill in the gaps, and show the steps, between meanings 1-4 and 5? The Oxford Latin Dictionary didn't expatiate on the semantic shift from 4 to 5, and skipped the steps!

I scanned Oxford Latin Dictionary (2 edn, 2012, OUP), p. 396.

 

[kizolk]

I think it's rather straightforward (which doesn't necessarily mean it's the right explanation!): if you're free to come and go, it pretty much means you're on leave of absence since... well, you can come and go.

 

[Laurentius]

I thought it had more to do with the meaning concerning a leave, a going away.