I work in a company that makes a range of measurement devices that talk over serial port. Some talk UART, some talk RS232, others talk RS422. I need to be able to test several of those at the same time - or maybe not, but when I'm sitting at home and working remotely, I like to have one of each kind already connected, ready to use. That's one USB port (for a FTDI USB-to-serial converter cable) or real RS232 port connected per device.

All those devices also have a second UART serial port to dump tracing information onto. Most of my test devices have the trace serial port connected also. That's another USB port per device.

And then most - not all, but most - have a JTAG programmer attached to them, to debug then and reflash their firmwares. That's one USB port for each JTAG programmer.

And I have several programmable bench power supplies controlling power to several batches of those devices. Each one of those power supplies uses one USB port.

And I have 3 cameras watching the goings on with those devices, one per USB bus (Linux won't allow more for bandwidth reason) to make alignment easier.

And to debug some of the devices, I have them talking through "snoop cables", i.e. a regular serial cable to control the device, but with the Rx line connected to a second cable's Rx line, and the Tx line connected to a third cable's Rx line, so that, by watching what comes through the 2 snoop cables, I know exactly what gets transferred to / from the device, if I have any doubt about what goes on at the hardware level.

And then I have a couple of USB-controlled precision tilt tables to align 3 of the devices. That's 3 more USB ports - although the tilt table's controllers also act as USB hubs, so I get two USB ports back for every main one I use.

And then I have oddball devices connected, like a servo controller for another application, a USB-to-serial cables out of which I only use the RTS line to turn a laser pointer on and off.

And then a trackball, a keyboard, a 3D Space Mouse for CAD'ing...

This is one of my USB hubs:

I've been at the same company doing this stuff for years. Things add up over the years 🙂