In the worst case, moisture intrusion and loss of lubrication can cause bearings to rust. If your bearings came with non-removable shields, they are at greater risk of contamination if you remove the shields to facilitate regular maintenance. Looking for any possible advantage, many racers install freshly cleaned and lubed bearings just before a race. For easier access to maintain the moving parts, they purchase bearings that have removable shields. They may even leave the inside shield off to make frequent maintenance that much easier.
Racers also lubricate with oil.
Therefore, the cleaning and lubrication has to be done religiously. It's one of the many prices racers are willing to pay to win. But, if you're a recreational skater like me, you skate more religiously than you work on your skates. I barely have enough time to skate, much less give my bearings a regular shower and shave. I've never removed the shield from a skate bearing, let alone lubed one.