I’ve started to notice that there’s not much oil on the barrel after I’ve done a few dry fire sessions. I’ll add a little drop when I feel like it’s somewhat dry.
Is this something everyone does, is it really necessary, am I just being goofy? Is it all three 
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I would think it would depend on the type of gun and how much lube it likes to stay running. I have not owned one in a while, but pretty sure you HAVE to oil a Glock at least once every 5 years, 1911’s tend to be a bit more needy. 
Unless the gun maker says otherwise, I see no problem using a little lube on any dry metal to metal contact.
If you dry fire the oil out of a gun, I’d encourage you to find another hobby. 
I have no science to back me up but logically the carbon from a round being fired is what “uses” up the oil. So without firing a round I honestly couldn’t imagine how many times you’d have to dry fire to “wear it out”.
As mentioned by @Fred_G it mostly depends on the firearm.
I’ve been dry firing PPQ, CZ-P-01, M&Ps - they run DRY without any harm.
I’m not sure about 1911 style, I’ve been told they like oil… so I lube them and never run dry.
To be honest I do not think much about it anymore, using small trick during cleaning process. I use “Hornady One-Shot Cleaner”. It evaporates fast, leaving a light protective film with some lubrication. Non sticky and oily at all. Perfect for dry fire practice. Once I’m done with practice, I put some extra lube on the barrel.