I use to use aluminum more before but I like parchment paper better. Works good.

Never had a sticking problem.

and the food stuck. No, not cookies, ptobably sliced potatoes coated in butter (and garlic and thyme)

never oil/butter the paper, no sticking problems.

told me the secret to their "creamy made without cream" veg soups: they roasted the veggies, then pureed with broth ...

If I'm baking, I use parchment paper; if I'm roasting, I use foil. As far as whether to grease or not to grease, I normally follow the recipe instructions, but from my own experience, I've found that it's not usually required for baking. But you can do it however makes you feel most confident.

They are good to about 500F, no waste, and cleanup is easy.

as long as you poke some holes in the sausage so it doesn't explode. For this one, either option would work. The advantage to parchment paper is that nothing sticks to it, and I'm looking at you, coconut macaroons. It's also better for things "en papillote," nobody gets a piece of aluminum on a filling that way (ow!).

We eat a lot of roasted veggies.

When roasteing a half-sheet pan full of veggies, I wrap the pan in aluminum foil to prevent any oil dirtying the pan and then add a sheet of parchment to prevent sticking.

I think of the foil as the barrier to keep the pan cleaner and the parchment as the layer which does the anti-stick work.

I also line my baking pans with parchment to lessen sticking and to ease removal.

Will parchment alone not accomplish this?

it fails to keep the sheet clean.

And a belated welcome to DU.

You have already made your mark.

but today I prepared cod placed on top of roasted potatoes which were coated with butter and the recipe did call for parchment so I followed your suggestion: parchment on top of foil and everything came perfect.

just my personal preference