Kind of a silly question, but I’m curious about it.
With Lovelace becoming the default UI in the coming weeks, I’m wondering if my groups.yaml will continue to serve any purpose as I was only using it to group the UI elements.
Will groups.yaml continue to serve a purpose after we all move to lovelace?
Entity groups pretty much
What are they useful for? I tried making one with a bunch of speakers so I could turn them all on and off at once but it didn’t work.
It should work but pretty much that. You can use the group to do mass actions, or to summarise states, eg people_home = home if just one person is home in the group.
I use groups to ‘group’ things and then I can use an automation to act on that group… like a group of automations for instance that if I am going away for a few days, I want to disable a bunch of automations so I have them in a group and then another automation to toggle the whole group on or off. Other than that, in a lovelace world…
So the question stands.
For example, I have a group of sensors and iterate over them in my automation to do something as I don’t want to hard-code these sensors in the automation.
I had to replicate that group as a Lovelace card and now ask the same question - what’s the point of groups and how to use Lovelace cards instead of them?
I’m new to Lovelace so please bear with me 
It does seem a bit obsolete now with Lovelace cards doesn’t it. I personally have only one defined group remaining and that is for all my Amazon Echos for group vocal announcements, so I don’t even have a groups.yaml anymore, just a simple, single group: definition in my configuration.yaml.
I just commented them all out except my all speakers group too