In article ,
"Percival P. Cassidy" wrote:

I took down a couple of pieces of beat-up sheetrock and found that many
of the cavities were almost completely full of pieces of sheetrock.

I have seen this a couple of times over the years.

Any good reason why a builder (or remodeler, perhaps) would have done
this?

No.

The only thing I can think of is that it saved them the trouble of
carting the offcuts away and perhaps paying to dump them.

The landfill charge difference would be negligible. It is probably due simply
to a shoddy "rocker" too lazy to collect the myriad small pieces and walk them
out to the dumpster.

I suppose they haven't been doing any harm, but they are a pest if I
want to install an old-work outlet box in a section of wall where I do
not remove the sheetrock.

I NEVER thought of that but you are right on. That would surely be a PITA.
--

JR