In the case of prefabricated cellars, only one side of the wall is formwork-smooth and thus paintable. In addition, there are deep joints between the elements, also on the ceiling. You definitely want to do something about that, otherwise it looks really very rustic. For a purely utility cellar, you can possibly leave it as is. On the other hand, one can say that with masonry, plastering is not necessarily required, e.g., when building with [Kalksandstein Sichtmauerwerk].