Network separation and VLANs

I'd like to better understand why HogNet and FixtureNet need to be on separate networks. What is the failure mode we are trying to avoid? Is it collisions on the switch? Is it internal to the network interface on the console? 

The reason I ask is it's very beneficial to me to only have to run one cable for both HogNet and FixtureNet as I'm constantly mobile and have to move my setup many times a day. To that end, I'm playing around with 802.1q VLANs and I've experienced no issues when they are on separate VLANs. I've also experienced no issues when the VLANs are combined in such a way that the endpoint can access both HogNet and FixtureNet, but the console's ports are still separated from each other in this setup. Should I expect to have an issue in that situation, or should it be ok?

I usually only use HogNet to connect a remote hog4pc console, no license, no server or virtual DP8k, but on bigger setups I'll have a DP8k on that network. I don't know if that's relevant as I don't know what kind of failure mode we expect.

Thanks for your help!