In a lot of environments, you can at least choose to restrict what networks can be used to manage equipment; sometimes this is forced on you because the equipment only has a single port it will use for management or must be set to be managed over a single VLAN. Even when it's not forced, you may want to restrict management access as a security measure. If you can't reach a piece of equipment with restricted management access over your management-enabled network or networks, for instance because a fiber link in the middle has failed, you can't manage it (well, remotely, you can usually go there physically to reset or reconfigure it).
You can cross-connect your out of band network to an in-band version of it (give it a VLAN tag, carry it across your regular infrastructure as a backup to its dedicated OOB links, have each location connect the VLAN to the dedicated OOB switches), but this gets increasingly complex as your OOB network itself gets complex (and you still need redundant OOB switches). As part of the complexity, this increases the chances an in-band failure affects your OOB network. For instance, if your OOB network is routed (because it's large), and you use your in-band routers as backup routing to the dedicated OOB routers, and you have an issue where the in-band routers start exporting a zillion routes to everyone they talk to (hi Rogers), you could crash your OOB network routers from the route flood. Oops. You can also do things like mis-configure switches and cross over VLANs, so that the VLAN'd version of your OOB network is suddenly being flooded with another VLAN's traffic.
(I am the author of the original article.)
You can cross-connect your out of band network to an in-band version of it (give it a VLAN tag, carry it across your regular infrastructure as a backup to its dedicated OOB links, have each location connect the VLAN to the dedicated OOB switches), but this gets increasingly complex as your OOB network itself gets complex (and you still need redundant OOB switches). As part of the complexity, this increases the chances an in-band failure affects your OOB network. For instance, if your OOB network is routed (because it's large), and you use your in-band routers as backup routing to the dedicated OOB routers, and you have an issue where the in-band routers start exporting a zillion routes to everyone they talk to (hi Rogers), you could crash your OOB network routers from the route flood. Oops. You can also do things like mis-configure switches and cross over VLANs, so that the VLAN'd version of your OOB network is suddenly being flooded with another VLAN's traffic.
(I am the author of the original article.)