I have heard the exact same thing. Any patent attorneys on here who can explain the things that can go pearshaped?

Yes, getting the inventors wrong is a bad thing. Every inventor has an ownership of the invention and initially has an ownership of the patent that results from it. Usually when a company files a patent, they make sure they get all inventors to sign assignments which give their rights to the invention and patent to the company. But if they did not get all inventors to sign, and an unnamed inventor can later prove that he/she was actually one of the inventors, then the unnamed inventor will be held to be part owner of the patent and any inventions that are listed in there.

Thus, a company can invest tens of thousands of dollars into a patent and millions of dollars into developing the patented technology and then an unnamed inventor may appear out of the blue and claim ownership.

So yes, it is important to name all the actual inventors.

BTW, this is not legals advice, just academic, theoretic discussion. There are many more complicated issues that can and will come up in real life, so I hope nobody actually tries to extract legal advice from this.