Harm? Other than to your nose 'n nerves, not that I can think of. When I bought my '82 turbo it was because of a plugged cat (they thought it was a failed turbo). The car would only go about 10-15 mph, sorta like limp home mode for K-jet. And it had that sickly sweet, exhaust-like smell like some rotten fruit was burning in the muffler. But it wouldn't drive at all.

So if your car runs OK on the highway but still smells, I'd keep in mind that it might be crummy gas, as Smitty suggested.

The other thing -- we're trying to diagnose a problem based on our interpretation of your description of a smell. These are all qualitative exercises layered upon each other. It would be FAR better for you to get a solid, first hand evaluation by an experienced mechanic. (Would that be first nose evaluation?)

For example, suppose burning brakes pads smelled "sweet" to you and you described the small as "like exhaust" (because the pads were burning). Then our diagnosis would be AFU because of misinterpretation. And there would be harm if the problem was not addressed quickly.

Remember the guy who wanted to change his motor mounts by jacking up the oil plug, and his stupidity was our fault?
--
Don Foster (near Cape Cod, MA)