Well? 
Keeps the pot from overboiling.
I thought it was to keep it from sticking together.
Aye. .
I don’t, and my pasta neither boils over nor sticks together.
I do not, nor do I add salt.
Yeah, that.
I put salt in the water, but never oil.
Not sure why you would. It will just sit on top until you dump it out, then the oil is going to prevent the sauce from sticking to the pasta. Just not a good idea in general.
I don’t. You shouldn’t either.
This.
This is what I thought. And it does seem to work. I suppose if you’re going to stay in the kitchen with a watchful eye, it’s not necessary though.
I do not because it makes it harder for the sauce to stay on the drained pasta. Of course, pasta is good in it’s own right, but is really just a delivery mechanism for sauce. Why mess with that?
Most professional chefs that I’ve seen or have read say not to, for the reason @snowthx stated.
I use it in the microwave on one particular dish. Adding the noodles and the sauce and the water fills the bowl just a little too much, so a spray of oil on top keeps me from having another mess to clean up.
Dietary restriction reasons, I assume.
There’s more oil in the sauce than in the correct amount of oil, a few drops IMHO, as boil-over insurance.
Sort of. I have hypertension so in my case lower salt is good. But I also have a weird salt perception. I’m not good at “salting to taste”. A salt grinder is on the table for my gf’s use, and I’ll sometimes ask her to taste what I’m cooking and salt it to her taste.
In spite of knowing the downsides, I used to do it to prevent boil-over on an electric stove as reducing the heat to the “boil/but not too much” level took too long. Now that I have induction (and the same would have been true with gas), it’s easy to avoid boil over, so no oil is used.
That’s the only reason to do it. It does work, but I just use a larger cooking vessel, so I don’t need to worry about boiling over. (Or, actually, these days I just start with pasta in a smaller amount of cold water from the beginning and bring it up to a boil until done.)
Someone posted years ago that the only use for oil was to keep cooked pasta from sticking to itself. I continue to squirt olive oil into boiling pasta much as some folks throw salt over their shoulder.
I don’t put oil in the water, nor salt but ater draining I do dribble a little into the hot pasta to help it separate.
As long as it is only a little it makes no appreciable difference to sauce adhesion.