MagSafe 2 85W on a MacBook Air (13-inch, 2017)

I've run into people in the the Apple Support Communities who say they have never run into problems with doing that.

I have. I sold my 85W adapter to someone who erroneously told me they had a MacBook Pro.

They came to me after plugging it in their MacBook Air, and burning the power port.

Not everyone will experience that. But it is a caution tale that has to be told, that the risk exists that it is higher because the cord provides more power. Whether a surge caused it, a lack of proper grounding, or older poor power setup in a house with fuses instead of circuit breakers, we'll never know.

But suffice it to say, Apple's article does recommend using specific wattage adapters for specific computers:

Identify your Mac power adapter - Apple Support

Yes, that is perfectly safe. We do that for my organization's Macs.