it will disturb rustproofing. definitely. Thats why at the beginning of spring, dealers offer to pressure wash your car. To remove the rust-proofing and all the contaminants (salt, mud, etc)
And if your going to be doing repetitavely say once everyday or once a week... After a month, there shouldnt be any rustproofing left.... = bad.
unless you grease it up yourself afterwards.... You should just spray it with a hose, not a pressure washer.