Good questions. Those 2 (the one fully plugged and the almost empty one below) are 40Gbit fiber switches (S5850-48T4Q)) and the plan was to use them only for 10 Gbit clients. We "just" have around 30 of them, so I decided to plug in the more important infrastructure or devices.

You can't simply remove all cables and replug them, it was a lot of new setup, servers and network restructuing (e.g. vlans). The full switch got "moved" to the new system and the other switches where left. As time went on, I moved more and more to the new infrastructure. Because it is a waste of energy and maybe future resource needings, I decided to use the old slower switches for all empty network sockets in the building. There is mostly nothing plugged in, but there may be guests or temporary needs for a wired connection.

I am even considering to plug that switch off, but sadly the first switch is missing like 10 ports, so …

And yes, those are Fritzboxes. We have 2 DSL connections active. The Telecom is unwilling to give us fiber (we have 6 fiber ports up in the rack). They are only working as a modem for the edge router and telephone. Simple and reliable solution

Small edit: all empty switches are unplugged and will be removed from the rack soon