I have said before that USB is the best and worst thing to happen to AV. It is a wonderfully useful technology with a consumer-friendly connector. It just works, or at least that is what we would all like to believe. On a complex design, that belief is where it breaks.
Most AV drawings show the USB signal path. Very few show how many hubs that signal passes through. The common understanding is that USB allows 7 hops, which sounds like plenty. The spec allows 7 tiers, and the host's root hub and the device at the far end take 2 of them. That leaves 5 hubs between the computer and the last device. Faster signaling in USB 3 and USB4 adds no depth.
Counting boxes does not give you the hub count. A camera that presents video and audio as one composite device adds no hub. A conference bar with a hub built inside takes 1 tier. A dock often takes 2. An Extron extender pair can present as 3 hubs at its default emulation and pairing settings, which is documented, configurable behavior the design has to account for. In a simple huddle room none of this matters, because there are 2 or 3 tiers to spare. The rooms that run out are the ones with the most equipment and the most senior people at the table.
Earlier this year we completed a boardroom table that leaned heavily on USB. It was designed to the count and commissioned clean. Some time later the customer called because several of the table's USB inputs had stopped working. When my team arrived, we found an inline USB charging hub that had been added so members of the executive team could charge their phones. That one extra tier pushed the far devices past the limit. Nothing we installed had been touched.
The system was right when it was signed off, and it failed when someone assumed USB would behave the way it does at home. Network hops and cable lengths go on every drawing as a matter of course. USB topology belongs on that same drawing with every tier counted.