AusRenovation

Yup.

I use glue-only for an above ground i want to break at some point and recoup parts. I use primer when i want it permanent. Glue only a strong twist can break it. Primer you're gonna have to get the saw.

To put it in simple terms, the priming fluid sets up the PVC cement to do its job properly. The primer acts as a cleaner, removing grime as a PVC cleaner does, and it also softens the surface that it is applied on. PVC pipes are joined together through a change in their chemical composition.

(High) Pressure it likely matters, you want a strong bond. Stormwater/downpipes, probably not.

Not a plumber.

I just did a quick websearch for both these answers, try a deep dive on some Reno forums or similar, find a plumber or chemical expert as to why it's important.

Another one:

https://redlib.perennialte.ch/r/Plumbing/comments/camh2c/is_pvc_primer_reeeeeally_necessary_when_youre/

Quote:

You may as well just silicone the pipes together.

The primer softens the pipe to prep for the fusion process.

Without primer the glue is essentially just a gap filler.

That oatey cleaner you are talking about is for ABS pipe usually.

ABS doesnt require a primer but is often suggested to use that cleaner prior to application.

A link:

https://www.plumbingsupply.com/the-great-pvc-primer-debate.html