Pressure regulators & main shutoff valves
Failing regulators and shutoffs replaced before they fail worse.
A pressure regulator that's failed high stresses every fixture and appliance in the house; a main shutoff that won't fully close leaves you stuck in an emergency. Both get tested with a gauge and replaced before they cause damage, not after.
Related work
Anything unusual about the job is talked through with you before a tool comes out of the van.