What's the latest thinking on splitting SSIDs between 2.4 & 5GHz frequencies? I have around 30 smart switches, lights & other home automation devices which need a 2.4GHz connection and have set them up with the router in 2.4GHz mode only then turned on 5GHz again once they are connected. Are there any advantages to keeping the 2.4GHz frequency as a separate SSID or is it best to let each device decide which is the fastest connection using a shared SSID?
There's no "latest thinking" on SSID intent...
It's a bit of a touchy subject, much like Parental Controls and "what wifi channels I should use" kind of thing - people have a lot of different opinions...
I was a partner in the IEEE 802.11 working group, and the intent there was that SSID's define the network relationship to the LAN/VLAN...
It was never our intent to have segregated SSID's for the
same LAN/VLAN segment irrespective of band class...
That being said - let's say we want to have different access policies - one for guests, perhaps one for VOIP solutions - there's where addtional SSID's come into play - e.g. Guest has a specific policy and associated access control to allow access to internet, but deny access to intranet resources. Same goes with VOIP applications, as in the enterprise the IP deskphones and walkabout wireless handsets have specific QoS requirements, and again access control policies come into play.
When done properly, it works pretty well all told...
Let's be plain here - most WiFi devices in the house don't move around much except for mobile devices like handsets and tablets - and there, both Android and Apple, which define a vast majority of devices, are pretty good at making decisions on which radio to use - providing of course, the SSID is the same across the bands.
As you see in the thread here - there's still a lot of "old-school" thinking about Wireless that goes back to the mid-90's when 802.11b/g/a were in vogue.
On a single LAN/VLAN segment, whether single AP, or multiple AP's, setting up different SSID's per Band - this will likely ensure that without user interaction, the device has a good probability of being on the worst performing radio.
Best approach, in my opinion is to use common SSID's, and for tri-band* (e.g. 2.4/5/6GHz) use WPA2/3...
* note that I say tri-band, not tri-radio - there are dual-band routers that have 3 radios, that doesn't make them tri-band except for marketing purposes...
NOTE - There is a use case where common SSID's can be a challenge, and I've experienced it first hand - that is configuring 2.4GHz IoT devices, namely TP-Link Kasa Smart switches, where if the phone was on 5GHz, I couldn't configure the switch out of the box - by disabling 5GHz temporarily, I was able to configure the devices, and once done, turned on my 5GHz radios and everything was fine.