Brakes and Swivel Locks are common add on's for industrial casters, each option offers additional benefits to a traditional caster.
Brakes when engaged, keep the wheels from turning on the caster
Swivel Locks convert a swivel caster into a rigid caster but add the benefit of locking the rigid at additional angles (versus the standard 180* angle of a rigid caster)
Both brakes and swivel locks also add safety benefits
Brakes ensure that the cart or rack will not roll away or move when unattended, especially if the unit is being unloaded manually
Swivel Locks make it easier to control the cart or rack when rolling and can be used to ensure wheels stay perfectly parallel when a cart is parked (this is beneficial because it requires greater force to start rolling a cart when the wheels are parallel).