The truth is any of the above, it all depends on what you want. I have a Kickr Core with Zwift running on an iMac. I have a set of Wahoo sensors for speed and cadence and use neither for Zwift, but I have cadence coming from my Assioma pedals. I also have the Wahoo Tickr HR strap. All of the sensors and the Core support both BT and ANT+, and I have an ANT+ dongle on the iMac but at this point it is unnecessary. I mostly used it for my old Garmin HR monitor that was only ANT+. The reason I keep it plugged in is that all of these devices can be finicky. Some days they connect instantly, other days they just don't. Bluetooth has its own issue in that a nearby phone can connect to a device and that prevents my computer from using it. With all of the devices around it just takes a lot of checking to see what has it.

In Zwift I don't find myself looking at cadence so much but when I go on The Sufferfest their videos all specify a target cadence. In Zwift I tend to use the Kickr in simulation mode where it tracks the climbing grade, and in The Sufferfest I use ERG mode, which keeps power at the specified amount regardless of cadence. Different types of workouts that complement each other. You can do Zwift in ERG mode using workouts but I find it boring since it removes some of the social aspect of being able to ride with others.

Everybody has their own way of using these things, and I don't feel like my way is the best way.