It's a blood bio bank, not a DNA database - although the latter can be created from the former, of course. As far as I know it's only been used once by the police to identify a criminal, they used it to confirm the identity of the person who killed the minister of foreign affaris(?) Anna Lind.
The main purpose of the biobank is to detect rare disases in newborns, see https://en.wikipedia.org/wiki/Newborn_screening
It's not mandatory to take the test on your newborn, and it's possible to request your sample be destroyed.
There has been talk of opening up the samples to police use, but so far it's been decided that the downsides would overweigh the benefits. One of the fears is that opening up the samples for other use would mean fewer infants will be tested (increasing suffering for those who miss an important diagnosis), and some adults will reques their samples be destroyed (reducing the research value of the data set).