Brine is worse than rock salt
Liquid de-icer is sprayed as a film, which means it coats and clings instead of bouncing off. It also stays hygroscopic — it pulls moisture out of the air and keeps a damp, salty layer against bare metal long after the roads dry.
You cannot see any of this from the driver seat, which is exactly the problem.
Where it does damage
Frame rails, brake lines, fuel lines, suspension mounts, exhaust hangers, and the inside lip of every wheel well. On trucks, the seam behind the rear bumper is the classic first place rust shows up.
None of those surfaces get touched by a hand wash in your driveway.
What to actually do
After any ice event, run an undercarriage rinse within a few days — it is included from Buzz Plus up. If you drove I-35 during a storm, do it twice that week.
A ceramic sealant on the painted surfaces helps too, since salt has a harder time keying into a slick sealed layer than into bare clear coat.