What additional purpose do fixture traps serve?

Fixture traps serve multiple purposes within a plumbing system, and one of their vital roles is to obstruct vermin, such as rodents and insects, from entering the building through the plumbing lines. The trap holds a small amount of water, creating a barrier that effectively blocks the passage of these pests while still allowing wastewater to flow through. This function is crucial for maintaining sanitary conditions and preventing potential health hazards associated with vermin infiltration.

The other options relate to functions that fixture traps do not specifically address. They do not improve water pressure, facilitate plumbing repairs, or enhance aesthetic appeal directly. The primary design of a fixture trap centers around providing a functional barrier as well as retaining water to prevent sewer gases from escaping into the living spaces.