There's the skeezy usage of them—citing the marketing claims as truth. (I totally forgot about the possibility of this usage, honestly.) Yes, nobody will let you get away with that.

But there's also the more literal way to cite a press release: as a primary-source claim by the company about what the company is doing or planning to do, like the group equivalent of a diary.

Obviously unacceptable: "Apple's new iPhone is the best ever!![citation to PR fluff-piece]"

Acceptable, I think: "Apple issued[https://www.apple.com/ca/newsroom/2017/06/imac-pro-most-powe...] an interrim press release on June 5th, 2017, claiming that they were working toward the release of a new "Pro" iMac model, as a supplement to professional users who are waiting for the next generation of the "Mac Pro" product line, which they mentioned as having been delayed."

It's a use/mention distinction thing. It's not okay to report the press release's claims at face-value, but it's okay to treat the press release as a primary source of information on the corporation's intentions, beliefs, claims, and assertions. It'd be similar to, say, citing the primary-source of a letter(s?) patent, as a source of information of a head-of-state's intentions, beliefs, claims, and assertions.

Or, to put that another way: any claims a PR piece might make are unverifiable, but the mention of the claim is itself verifiable—you can verify that the claim is right there in the PR piece, and you can verify that the PR department of the relevant company really did publish it, and thereby you can verify that the company is in fact making that claim... which can be an important thing to have in an article about them all on its own.