Is a basement in a single-family house useful or rather too expensive?

Basements today are not like they used to be. If you build a basement, then fully insulated with a floor and room height of 2.50 like the ground floor. Ideally also with a light well, etc. Then the floor will not be a dark storage room but a fully usable living area

Flat plot >800 m² and then I think I would build without a basement as well.

Terrible ... and then put the illegitimate unloved child in there

Or forum trolls

The basement rooms at the friends' places were always the best; at least theirs was always significantly bigger and you could be louder as well.

With the summer temperatures, it is also more pleasant in our basement.

Basements today are not like they used to be. If you build a basement, it should be fully insulated with a floor and a room height of 2.50 m like the ground floor. Ideally with a light well, etc. Then the floor will not be a dark storage room but a fully usable living area

Instead of light wells or something else, you can also simply build a raised basement, which depending on the federal state can significantly protrude above ground level.

By the way, in high summer I really appreciate having a sleeping place in the basement.

Personal opinion? We skipped the basement and instead invested in living space. This includes a fully insulated attic with 120m², and a cargo winch will eventually get all the basement junk up there. We located the utility room on the upper floor, right where the laundry is. The technical room on the ground floor is only 10m² and therefore doesn’t really take up much of the sacred ground floor. Bicycles go where they belong, in the garage, just like the stroller, scooter, etc..... The garden stuff goes into a garden shed. Our last refrigerator, which is being moved to the technical room, cools the drinks. All in all, the extra living space was cheaper than a basement. So why have a basement?

A little anecdote on the side, two weeks ago it rained very heavily in our future street. The neighbor’s basement flooded through her basement entrance..... good thing we are "only" building a slab foundation.

You ask why a basement, after you have converted 120m² of attic + utility room + garage + garden house?