What a strange recommendation. I do research in CS theory and machine learning and I try to find arXiv preprints when I can, they are usually more complete than conference versions of papers. If you stick to papers from authors you know or to those from well-known conferences, arXiv is often times the best source.

This is an extremely wrong viewpoint. "Many extremely important* papers have been published on arxiv alone - no other publisher. Just off the top of my head, without looking, ELMo from allenAI (the paper that started the contextualized representations revolution for BERT/attention) is only on arxiv.

That sounds highly misleading. It is the standard preprint site in many disciplines. So you should take it as seriously as any preprint and conversely if a published article is not on the arxiv, that would be suspicious.

Many of the best papers appear an Arxiv first. In some fields, it is customary to put your preprint on Arxiv before/during the submission to the peer reviewed venue.

Arxiv is vital for quickly developing research fields.

Eh, there are plenty of actual pre-prints you can find on arXiv. Typical flow is you find a paper of interest published elsewhere then search arXiv for the same title, authors, etc. and can even find related work. A lot of publication isn't doing much in terms of genuine peer review but formatting, catching minor errors like grammar, typo, missing references etc. arXiv is great as a legitimate source for valid information tucked behind a paywall. It's not the only option but it's one of them (checking the primary author's personal site, researchgate, or associated research institutions repositories are also there, as well as contacting the author directly).

So the math, physics, and computer science departments of every major university should be ignored? What a brain dead comment.

I extend the same courtesy to this site.