Whats wrong with a wash and wax man?
The main issue is that, over time, it will coat your glass and it's a bit of a pig to get it off. If you've ever noticed glass feeling grainy or that it feels like it has fine ridges all over it, odds on it's owned by someone who uses a wash and wax product. It can actually stain glass slightly. It can build up on the paint and mute the finish.
It can also play havoc with some of the rubber seals around doors, windscreens, etc (which you obviously wouldn't ordinarily wax). Much better off using a quality, dedicated, high-lubricity shampoo for the paint and keeping the wax/protection step separate.
The protection they offer is FA but they do leave residual crap which is a big time waster when you want to get rid of it. No sense in applying a quality sealant/wax and top it with some cheap **** product.
With my car, I'll wash it weekly (at least) and, after each wash, go over it with a polymer QD which leaves behind a very fine, protective layer - that works as a sacrificial layer over the wax in the event of bird bombs, etc. The one I use seems to last about a week - helps the wax last longer, but doesn't build up as it also has light cleaners in it (though is most likely being removed by the next wash anyway. This also stops water spots, finger prints, and the one I use is anti-static, so does noticeably (though not significantly) reduce the amount of surface dust the car holds - it adds about 6 minutes to the wash process. It also amps up the gloss and leaves the paint super slick. There are also spray waxes, but these can build up and actually mute the finish over time.
I'll top wax coats up every 4th wash or so and generally rip everything off it and start fresh at least twice a year - more if I'm testing.
edit.. wow.. that went off topic!
