Energy consumption is essentially the same, as it's using the same radios.

For what it's worth, I have several SSIDs, each on a separate VLAN:

• my main one
• Guest. Has internet access but is otherwise isolated - Guest devices can't communicate with other guest devices or with any other VLANs.
• IoT Internet: IoT and home automation devices that need internet access. Things like Ecobee thermostat, Google speakers, etc
• IoT No Internet: Home automation stuff that does not need internet access. Security cameras, Zigbee PoE dongle (SLZB-06), garage door opener, ESPHome devices, etc

(to remotely access home automation stuff, I use Home Assistant via a Tailscale VPN)

Most of these have both 2.4Ghz and 5Ghz enabled, with band steering enabled to (hopefully) convince devices to use 5Ghz when possible.

This is on a TP-Link Omada setup with 2 x EAP670 ceiling-mounted access points. You can create up to 16 SSIDs I think.

I'm not sure that I understand the "more noise and energy consumption" part, since we're still talking about the same router with the same connected devices.

But I do have multiple SSIDs on my router. One is explicitly for IoT devices, and they don't have network access, so they are isolated from my computers, NAS, etc.

Are we talking main + guest network, or 2,4GHz + 5GHz, or something else?

Why would you want to do this, anyway? Or, as I as a developer regularly have to ask our sales people: what do you actually want to achieve that led you to this question?

Whether it has benefits is up to you, but from a technical perspective they're as expensive as VLANs, so basically free. It's the same receive and transmit radio, the only difference is that it broadcasts and responds to two network names at the same time. The maximum power consumption is the same: the max the radio will pull when at full load. The minimum power consumption has to be ever so slightly more since it needs to broadcast two network IDs, but those are measured in bytes and sent a couple times a second, it's negligible compared to the cost of just running the radio.

What benefit do you hope to get?

Separate subsets, segregated traffic. Easy to avoid crosstalk by setting channels further apart or using 2.4ghz and 5ghz

At home I have one SSID as a main wifi, and the other is guest wifi and IoT or other random devices.

Main downside is getting it setup and maintenance.

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:

10 acronyms in this thread; the most compressed thread commented on today has 11 acronyms.

[Thread #570 for this sub, first seen 4th Mar 2024, 09:55] [FAQ] [Full list] [Contact] [Source code]

Typically you have main and guest to isolate them You also have different networks for different bands because they use different radios (2.4GH and 5GH) with both having tradeoffs of range and speed. Some have triband as well so that you can isolate high performance devices because every device on a network increases latency slightly, and more so a radio only support one broadcast method at a time and will downgrade its self to the least common dominator for the devices connected to it.

I am worried that there is not really a benefit of doing that, just more noise and energy consumption.

If there wasn't a benefit, why would people (and pretty much every business) do it?

I remember reading a few self hosters describing having a separate WiFi for IoT devices, on a dedicated router (opensense) so they can prevent these devices "calling home". They are maybe other advantages like having different WiFi channels for these things

What benefit are you looking for? It shouldn't affect speed unless you are really hammering it. I'm assuming your talking about two networks on the same frequency (either 2.5Ghz or 5Ghz)

Lots of answers about use-cases of additional wifi networks, so I won't go into that. I haven't seen the downsides mentioned here, though. While technically you can run lots of wifi networks of off the same wifi router/ap, each SSID takes a bit of air time to broadcast. While this might sound rather insignificant since this is only a rather tiny bit of information transmitted, it is actually more significant than one might expect. For one the SSIDs are broadcast quite often, but also they are always transmitted at the lowest possible speed (meaning they require a lot more airtime than normal WiFi traffic would require for the same amount of data) for compatibility reasons. This is also the reason why it is a good idea to disable older wifi standards if not needed by legacy clients (such as 54 Mbit/s 802.11G wifi).

Having two networks is usually fine and doesn't cause noticable performance degradation, having 4 or more networks is usually noticable, particularily in an already crowded area with lots of wifi networks.