Dario Šariu0107’s shortcomings as a defender somewhat handicap what the Golden State Warriors can do with him as their back-up center.
Centers have responsibilities on defense that are extensive. They need to constantly defend pick-and-roll action; that requires knowing which coverages are being played. They need to stay close to the paint to wall it off; should someone fall through the cracks, he needs to be in proper position to contest legally.
Considering the kind of player Šariu0107 has been throughout his career, he’s far from the profile described above — mostly because he hasn’t been used in that manner for most of his career.