If you’re going from LA to SF you’re fine. You’d take the Coast Starlight to SJ, then you’d transfer to Cal Train, and that drops you off at the Transbay Terminal in SF which gives you easy access to BART or Muni and all of the streetcar and bus lines. Owning a car in SF is more trouble than it’s worth for a lot of people. I never owned one when I lived there.
Granted, SF is one of only a handful of US cities where this is true.
Heading south to LA would probably be a much bigger problem though.