A couple of possible ideas:

* Heightened risk of compromise in particular physical locations?

* Use in conjunction with something like TAILS so it's harder for someone who breaks into your computer to achieve persistence?

* Decreased risk of compromises that involve multiple machines attacking each other?

* Attackers may be wary of storing huge amounts of data persistently because the associated changes in storage media could be detected by forensic spot-checks?

(The third one probably requires that the forensic examination can get access to everywhere that the data could be stashed ... like nonvolatile memory inside onboard devices, not just the hard drive and main RAM contents.)

Wi-Fi can, and will, send data behind your back even if you're not connected to any network. Some of it is a part of normal protocol operation (and can be used to track you). Malware on your system could initiate connection without you knowing. And then a malicious actor targeting you personally may spoof a network you often connect to (e.g. local coffee shop) and exploit the default autoconnect to known networks behaviour. Hardware switches protect you from all the above.

You could be booting off a USB running something like Privatix during the time you have wifi killed - so that system would be air gapped whenever it is running. But if you trust Privatix you don't really need a HW switch.

Do you trust the wifi firmware though?