There are probably TWO best ways to tighten a wheel nut (axel nut), and it depends on whether you use a spacer or not.
If you do use a spacer, tighten the nut firmly. A free wheel will spin a few revolutions quietly and then stop. This is perfectly in order.
If you don’t use spacers you will have to leave a tiny play between the bearing and the nut. A free wheel will spin for a long time before stopping. This might seem good but is actually not ideal.
I follow the rules above and I’ll try to explain why below for the interested.
First of, a spacer, for those unfamiliar with the term, is a metal tube mounted in between the two bearings of each wheel. The spacer has two purposes, (1) it keeps the two bearings perfectly parallel and (2) keeps the inner and outer ring of each individual bearing in line. It does so by ensuring no other part of the bearing but the inner ring is under pressure. Same purpose as the speed rings you mount on each side of the wheel.
Any gap (play) between the nut and the bearing could potentially cause the nut to loosen, the wheel to tilt and you to be less in control of the board. I think the gap also causes the wheels to revolve a little slower once you are on the board. Any movement not in the spin direction means loss of energy. Many of those drawbacks are minor and probably don’t happen very often. But they nevertheless exist.
Not using spacers nor leaving a gap means the bearing balls are likely under stress which causes unnessecary friction. (The nut will extert a force on the inner ring of the bearing towards the center of the board, while the wheel exterts a force on the outer ring on the other side of the bearing and in the opposite direction.)
Testing a bearing by letting a wheel spin freely only makes sense if you use spacers and have tightened the bolt. It won’t spin for very long because bearings rarely do. However, they should be somewhat quiet.
Counting spins on a wheel with play doesn’t make any sense to me. The bearing balls can be squared on such a wheel and the wheel would still spin. It is the inner ring spinning around the truck axle. The second you stand on the board that wheel is stuck. That’s because with your weight there is a lot of friction between the axle and the inner ring, hence the need of a bearing in the first place.