There are two "categories" of pre-wax cleaners (as I understand it). "Paint cleaning" can be done via abrasives (basically ANY automotive polish containing some level of abrasive load). And paint cleaning can be done via chemical means alone.
Products labeled specifically as "pre-wax cleaners" sometimes clean via chemical means alone. And some contain chemical cleaning agents plus some abrasive, but the abrasive is so fine that they're often labeled as being "non-abrasive". Slightly deceptive, but what it means to you is that it's NOT going to cause a haze like a compound might, and it might even clean up some swirls in the paint. Obviously, you won't get any correction from a "chemical-only" pre-wax cleaner.
These specifics might be spelled out for you on the product labeling or they might not be. It varies. If it's not on the label, AG's ad copy might give some extra details for particular products.
If you plan on doing any polishing/correction work before applying LSP's (last step products, i.e. wax or sealant), a "pre-wax cleaner" isn't needed. You're essentially doing your own pre-wax cleaning with your polish or compound of choice (you're "polishing the dirt away" with an abrasive). But if you're not polishing/correcting, then a true pre-wax cleaner can be beneficial, particularly on older, neglected paint. Or if you simply want to ensure that old product residues are removed before applying a new wax or sealant.
Keep in mind that AIO's (all in ones) contain a "built in" pre-wax cleaner (I say that loosely). Some AIO's clean via chemical means, some via super fine abrasives, some have both. All lay down a wax or sealant. AIO's are a time saver and are great on daily drivers. They're nice for do-it-yourselfers that aren't necessarily "autogeeks" (those who just want to throw on a coat of "something" a couple times a year). Or for those that don't want to pay for a multiple step detail. AIO's require just one step to clean, polish, and seal (instead of two or three separate steps). The downside of AIO's? They're not for appropriate for extensive correction work (90-100% correction or even moderate scratches) and the wax/sealant element generally doesn't last as long as a dedicated LSP.
