themightytimah has a point, if you end up using compounds to cut down the clear coat, you'll get nearly anything a paint cleaner would fix (what about oxidation?). Personally, I use paint cleaner after my cutting compounds just to clean off any leftover residue and give a clean slate for my fillers and oils to settle on. It's a little anal, but it makes me feel better
However, if you won't be using any cutting compounds (only glazes and mild abrasive polishes), a paint cleaner will be good to apply beforehand to set the surface up.
As I understand it, it goes like this:
Wash
Clay
Cutting Compounds
Paint Cleaner
Mild Abrasive Polishes (swirl removers/fillers)
Glazes (oils and fillers only, things like #7)
Sealant
Waxes
Clay is going to remove elements that cannot be dislodged by washing (or semi-bonded paint contaminants).
Cutting compounds are gonna cut down the clear coat to even it out with any scratches/swirls that existed. It will also completely remove contaminents bonded to the clear coat surface.
Paint cleaner is gonna deep clean the clear coat, like micro-washing. If your paint is in very good condition you could skip cutting and just use a paint cleaner.
Mild abrasive polishes are going to help reduce the APPEARANCE of any surface defects that may still be visible (scratches or swirls that cutting could not completely remove). It will "cut" a little bit but it's mostly for rounding out swirls edges and filling in gaps with fillers. These also usually contain glazing properties to bring back shine.
Glazes (pure polishes?) are going to do nothing to correct defects, but just add luster and shine through the use of oils.
Sealants are used to lock-in your now perfect finish that the previous steps should have resulted in. There are many kinds of sealants but some are very durable and can help keep your finish very well protected and not evaporate quickly like waxes do. Many sealants also add shine. Remember if you used glazes with oils and fillers that you need to use a sealant that can bond to that type of oily surface. Some sealants cannot bond to anything but a clean surface.
Waxes are also a type of sealant but they tend to evaporate quickly. There are tons of waxes that do very different things. but if you find the right one or combination of waxes to use with your car color then you can add so much more depth and wetness to the look even on top of what your glazes/sealants provided. I use pinnacle souveran paste and pinnacle carnuba quick shine wax one after the other on my black car, and it's amazing!