I however heard about things like riding a bicycle without lights and being fined 50 bucks for that, which triggers asking for an id, which in it's turn triggers a 100 euro fine on top. In the story I heard the second fine wasn't actually given.
(but buying alcohol you need also a personal document)
Carrying it is practical and most Germans do carry their ID, but it's not a requirement.
The only time I need my ID is during elections, but I can also show the one I have in our government produced app.
Older people in Poland do carry those, mostly out of some kind of habit and some kind of fear that police might need it. I can drive a car and get a speeding ticket, and all I need police to know is my ID number (it is not the identifier of my identity card), which I know by hard, it consists of my birth date plus 5 semi-random numbers). I don't need my ID, my driving license nor my insurance data - everything is located in police database based on my ID number (or my license plate).
Bad sides of carrying it is that you might loose it, and that is a PITA, because you need to block it right away (someone might take a loan with it, happens I kid you not) by calling your bank or similar service.
So I take it out from my wallet (which I don't carry also) only when I go to the airport.
Same thing if they stop you for whatever reason and ask you for it.
Or your personalized public transport season ticket is only valid in combination with a government issued ID.