A normal hose pipe is inadequate in my experience, even with a hose gun they don’t shift much muck, they merely get the body wet. The reason for pressure washing (and snow foam) is to remove as much dirt as possible before doing a contact wash (this will greatly reduce swirls and dulling of the paint, because you are dragging less grime across it) - if you don’t care about fine scratches then you don’t really need to pressure wash.
The main cause of rust on cars is not water, it’s salt. The more of it you can remove, the better, and a pressure washer will assist. Obviously one does not spray a needle or pencil jet at a rubber seal or into a panel gap or at the light clusters - like any power tool a pressure washer needs to be used with care, so fan jets and 45 degree angles are the order of the day. I wouldn’t ordinarily recommend pressure washing a canvas roof, but I have a special low pressure attachment on my machine that shifts ingrained dirt without being harsh.
I have yet to see any ill effects of proper pressure washing - although an MOT tester did once jokingly threaten to fail my car for being too clean underneath. But each to their own of course, if you’re not comfortable doing something or don’t see the point of it, you’d be silly to then do it! And decent pressure washers with the appropriate attachments are not pocket money.