If Sheldon presented "slighty too loose is better than slightly too tight" then this may well be the very first time he's been caught being wrong. Ball bearings all need to operate with a touch of preload. The amount of preload is set by the load they will have to take, With our cup and cone bottom brackets and with wheel hubs where there are a lot of elastic elements between the two bearings the preload needs to be set with the amount of flex in mind.

In each case the goal is to NEVER have the balls lose contact with the cup or cone at any point in their rolling path while under load. If the preload is not high enough and things flex enough to let the balls run loose at some point then the balls will be shot forward in their path. It's just like a slippery pumpkin seed pinched between two fingers when this happens. And then the balls bang into each other or the cage and also hammer at the bearing track. It also puts all the load on the ball or two at the opposite side of the bearing instead of forcing the load to be graduated between the half of the balls on the load side of the bearing. Wear under such conditions is far more rapid than when some preload is maintained at all points in the path. And this isn't just for bicycles. It's a common factor in rolling element bearings in any field from the space shuttle down to our lowly bicycles.

So without making the balls feel like they are cogging and advancing in little steps set the preload so you can feel some resistance in the spindle that is over and above any seal resistance. Get a feel for the seal resistance while the cups are still too loose but close. Then preload the cup you're adjusting until you feel it is rough and cogging. Back it off until there is some resistance from the bearings but it's smooth in feel. That's likely as good as it'll get. Then re-check and adjust as needed to maintain this feel as you tighten the locking ring because it will tend to loosen things up as the cup and ring tighten up just as another poster above described.

Granted with a cup and cone setup and with the tolerances that can sometimes stack up badly it may not be possible to set the preload so the spindle feels the same way all the way around. But contrary to some other posts I would err on the side of being a hair tight at one spot instead of having any play at the loosest spot.

This preload requirement is even MORE important for something like a headset. If there isn't enough preload then the balls at the extremes will cause brinnelling of the tracks and then the steering gets all notchy feeling.