Rather than copy and paste the paragraph it might be more useful to have a look at the entire Lycoming Key Reprints - Operations. There's loads of good stuff in there:
http://www.lycoming.com/Portals/0/te...Operations.pdf
Throughout the UK we are taught (everywhere it seems, and as seen on generic type checklists from pilot shops) to idle our conti/lyco engines at 1200rpm, the thinking behind this is to reduce the chance of spark plug fouling. These engines idle smoothly enough at 800-1000, and it's quieter, less wear and tear etc, so why don't we do that?
There's a bit on page 66 which explains why
ifitaint...