As as general rule, bearings should be adjusted so they are as loose a possible, but without play, in the their working position. For a QR type hub, there should be play when out of the bike, but not play when mountend in the bike. A useful and educational test is to use spacers to act as dropouts. Clamp a the skewer on the spacers and then turn the axle with your fingers. You will be able to feel quite a bit of difference between the skewer being open and closed.