Could physically connect it but leave the port in a shutdown state (or tagged to a bunk VLAN); or leave out/disable firewall rules allowing traffic in/out for that segment. Much better options than just having it disconnected as the luxury of going TO a datacenter these days are not what they used to be. ....
Yup, use case matters. For me it's a home NAS so the inconvenience of having to reconnect the cable is minimal. Additionally, most of whatever I need to do can be managed from the console. My usual IPMI experience is limited to stuff I cannot do easily from the console or the FreeNAS GUI, such as the odd firmware upgrade or fan speed profile setup. In my use case, the risk associated with having an active IPMI interface vs. the reward suggests disconnecting the IPMI cable. I can see that being very different in a datacenter setup. However, I'd also spend a lot of thought re: securing IPMI and physical access in such a location due to the security implications.
Speaking of security, I've elected to drop the twinax DAC in favor of multi-mode fiber from the switch to the NAS. It increases my NAS' power consumption somewhat but it also electrically isolates the NAS (other than the power cable). Given the other upstream protections, that should make it much more difficult for nasty transients and induced loads from reaching my NAS. Similarly, my edgeswitch running the POE cameras is also only communicating via fiber to the rest of the LAN.
Most folk do not have to consider this, but our house is on a hill and lightning strikes have felled two trees within 100' of it. Lightning rods, massive cables, etc. may prevent damage to the home proper but induced loads during a hit can be incredible. When we rebuilt the foundation, I unfortunately had not yet heard of
Ufer foundations or I would have spent the weekends welding up connections instead of just tying rebar. Reinforced concrete makes for a great ground but a good electrical connection has to be there. The incremental cost to install a Ufer foundation once you go reinforced is close to zero.