I’m still not certain what the advantage of a managed switch is.

I’m sure there is one because they’re more expensive.

The only thing I was able to discover is that they detect a network loop.

There was a period when I was paid to look after a bunch of managed switches, and they had a variety of interesting and useful features but that's a large corporate-like environment (a University) and it was part of a research programme.

[This is back when IPv6 is relatively novel and so the refit of a large building with brand new high end Cisco managed switches was justified as research, also leading to a hilarious "bidding" process in which Cisco's lone authorised supplier tells us what the price is, which of course is completely unaffordable, then we tell a Cisco exec what we want to pay, then they calculate a research "discount" which we are to be offered so that magically we pay exactly this much to the lone supplier].

Feature I really liked 1.: Time Domain Reflectometry. Port #123 failed? Ask the switch, it says the fault is 19 metres from the switch, measure by eye or with tape, oh yeah, there's the problem.

Feature I really liked 2.: Port history. You can see at a glance that ports #120 through #140 are not in use now but with history you can see that port #130 and #136 were used last Tuesday night. Aha! The only thing these ports actually do is support a madcap arrangement where Astronomy run laptops on the roof for stargazing. They can just use WiFi! No need to run all this extra stuff.

For the research we had MLDv2 group multicast support - e.g. 80 people have 100baseT networking, 10 watch video channel A at 40Mbps, 10 watch channel B at 40Mbps, yet the network is only moving 80MBps (40 + 40) and their links only have 40 Mbps each, the 60 non participants have all 100Mbps free - in principle that could be done in a relatively dumb switch, but also at home scale it's irrelevant anyway, and even at corporate it's cool but hardly worth diverting serious effort when you probably don't need such a feature.

The killer application for me is that my wired Ethernet security cameras are on a VLAN that I firewall from the internet.

Vlan tagging at the port level is great. They probably do other things as well.

VLANs are often useful.