The only major draw-back to much relatively low power, low load ground
running of a fresh engine, particularly if it's got chrome jugs, is you run
the real risk of glazing the cylinder walls and it'll almost never break-in
(how much is much? I don't know).

Even a factory fresh engine with either plain steel or Nitrided steel jugs
needs to be run sorta hard initially to insure adequate combustion pressures
(high power and loaded) to force the compression ring(s) to seat properly.
(Check with any good book on aircraft engines for an explanation of how the
compression rings - particularly the first one, if there is more than one in
your engine, work).

This is one of the real "Catch 22's" for the home builder unless you can
take advantage of a service like Jack Kane's.

I once flew a friend's Piper 6 - 300 that had just had the engine overhauled
with chrome cylinders. We were instructed to tow the airplane to the
take-off end of the runway, let the tower know what we were doing so they
wouldn't delay take-off, start up and take no more than a minute to check
mags and prop and full power and then GO! I wasn't comfortable but we used a
10,000 foot runway so we could abort with plenty (?!) of room if needed.
After running at near max. power for a couple of hours (with some power
changes to keep the CHT's corralled), we reverted to a more normal
procedure, though it was recommended that the engine be run hard until oil
consumption started to stabilize, which took near 5 -6 hours, with complete
stabilization in about 20.

So, if your fresh engine has Orange paint smeared on the jugs somewhere (the
code for Chrome if memory serves - AP's help out here), beware of very much,
if any, low power run-ups - or you're looking at some premature cylinder
work.

Dan Schaefer