My understanding of PIMS --
it's not mandatory... ..
It's not a background check on employee or employer nor any clients or consulting firms....


it is simply a database that holds information about H1/H4 petitions ( and may be other cases) from USCIS.

Going to any embassy for interview with approved H1/H4 paper and other supporting documents doesn't suffice embassy that it's legit. Anyone can print and produce those documents these days. SO embassy verify this information through USCIS. I am not sure if they directly hit USCIS database or portion of data gets synch to the embassy and they locally verify that in their database.
In each case, they just verify that the person claiming H1/H4 beneficiary is a legit case and sometimes it takes time to verify this.

In both cases of my H1 stamping in Nepal, a simple email to embassy was enough to get a reply from them saying that my PIMS was updated.

Benefits - Before interview, they have verified your case, now it just a matter of YES or NO and this should avoid few days of delay in case they don't have your information from USCIS.

Hope this helps...