Shields and seals help keep dust, moisture and debris away from the moving parts. Different designs balance protection, access for maintenance and ease of cleaning.
Protection matters
If you skate outdoors, commute or ride dusty spots, a protected bearing can be a sensible choice. No shield makes a bearing invincible, so care still matters.
Do not pry casually
Only remove a removable shield when you know how it is designed to come out. Damaging the shield can make the bearing harder to protect and maintain.