Personal machine as in a machine that you use for anything other than work for that particular client.

The same goes for putting anything personal on a company issued device, such as signing into your private email.

It is a problem in all circumstances. The problems may not always manifest, but if they do, you’ll be in deep trouble.

Problems range from the mild; company has mandatory tooling that takes control of your machine. To the extreme; offices get raided and equipment seized indiscriminately.

General assertions are fine. The exercise of whether to follow them up with research is left as an exercise to the reader.