The meaning of clay bar is remove thing that on the paint, right?
let's say you washed, used clay bar, polished, and waxed your car one or two weeks ago. and you have to clean it up this weekend, but the car is quite shiny , do I have to go through all the steps again? of course, washing, but are the other three necessary?
No, in fact it would probably be harmful to repeat claying and polishing for no reason. Use clay and polish it ONLY if it needs it. Depending what kind of sealant/wax you are using you might not even need to re-wax it (but could if you want). Just wash and maybe use quick detailer.
Clay bars remove embedded grit and contamination.
Polishes remove swirls, scratches, etc.
Clay, polish, and wax isn't a "system" like Zaino or something!