Lip bumper is used for:
Lip Bumper
Lip bumper is an appliance that makes use of the tonicity of the lip. The lip trap and excessive lip activity can be helped with a lip bumper  which prevents lip pressure on the lower incisor; their labial position gets normalised with tongue pressure. The lost arch length can also be gained with this method.
Key Concept: 
The lip trap and excessive lip activity can be helped with a lip bumper which prevents lip pressure on the lower incisor.
Reference: Orthodontics: Diagnosis and Management of Malocclusion and
Dentofacial Deformities 3rd ed Om P. Kharbanda pdf no 736
Mouth breathing
Nail biting
For lip biting & hyperactive rnentalis
All of the above