Yep, nothing like gettting the rated blade tip speed [i.e. full throttle] for perfect cut through a wide range of speed! Even if full throttle doesn't help mowing time [I'm betting experience will have an exponential effect there], it should help longevity.
Most [yes, pretty ambiquous term] air cooled engines in mowers are designed to run full throttle for proper cooling. I only run less in a couple situations [no particular rules, may not even be right, just hybrids of my strange mix of engine knowledge]:
1) 1/2 throttle for 10sec to a minute after startup to let the oil circulate before full throttle [some splash lubes or oil-fuel mix may or may not have benefit here]; I like at least a minute total of warm-up before mowing, but once at full throttle I consider driving time ok. If the book doesn't say different, I revert to this [and often do anyway].
1.5) Right [5 seconds?] before turning off the key [after about a minute or better of cooldown at full; I count driving as cooldown time too]. But read your engine book; to reduce backfire, the shutdown may require full throttle.
2) I'm also guilty of throttling down for a few seconds to better hear somebody yelling at me through the ear plugs. /forums/images/graemlins/blush.gif /forums/images/graemlins/grin.gif
I did read a somewhere [don't think TBN] where a couple proffesional guys were running 3/4 to save fuel, but I have to wonder if these weren't situations with small lots or cool climates where the engine never got much heat anyway.
Happy mowing!