Controllers are required to solicit PIREP information so they keep knowledgeable of what is happening in their sectors and so they can inform aircraft of potential problems. It is a required duty, but somewhat low on their list of duty priorities.
From their manual ATP 7110.65U
2−6−3. PIREP INFORMATION
Significant PIREP information includes reports of
strong frontal activity, squall lines, thunderstorms,
light to severe icing, wind shear and turbulence
(including clear air turbulence) of moderate or greater
intensity, volcanic eruptions and volcanic ash clouds,
and other conditions pertinent to flight safety.
a. Solicit PIREPs when requested or when one of
the following conditions exists or is forecast for your
area of jurisdiction:
1. Ceilings at or below 5,000 feet. These
PIREPs must include cloud base/top reports when
feasible.
TERMINAL. Ensure that at least one descent/climbout
PIREP, including cloud base/s, top/s, and other
related phenomena, is obtained each hour.
EN ROUTE. When providing approach control
services, the requirements stated in TERMINAL
above apply.
2. Visibility (surface or aloft) at or less than
5 miles.
3. Thunderstorms and related phenomena.
4. Turbulence of moderate degree or greater
5. Icing of light degree or greater.
6. Wind shear.
7. Volcanic ash clouds.
8. TERMINAL. Braking Action Advisories