What is a panel wipe and what does it do?
A panel wipe is a solvent-based spray that removes everything sitting on top of the clear coat: polishing oils, old wax, silicones and the fingerprints you did not notice. It cleans nothing you would recognise as dirt, which is exactly why people skip it. What it leaves behind is a chemically bare surface, and that matters twice over, because protection can bond to it and you can finally see the paint as it really is. Every product on this shelf is a variation on that one idea.
Do you have to degrease before waxing or coating?
For a coating, yes, without exception. For a wax or sealant it is the difference between weeks and months. Compounds are full of lubricating oils, and those oils are still on the panel long after the residue has been buffed away, so whatever you apply next bonds to the oil rather than the lacquer and leaves when the oil does. Skipping this step is the most common reason a new coating stops beading after a fortnight.
How do you know when paint correction is actually finished?
You wipe the panel and look again. Many compounds fill fine scratches while you work, so paint straight off the machine flatters you and some of that gloss is oil. A wipe with FINAL INSPECT V.2 removes the film and shows the correction as it will look in three weeks' time. If defects come back into view the panel needs another pass; if it still looks clean under a torch, you are done.