Meinolf's theorys are basically correct but it's just as much a matter of practicality and feel though. A lot of whats been explained can only be ratified on the dyno, flow bench and via logging lambda. One of the benefits of the Ducati Desmo system is that it allows faster opening of the valves because the rate of acceleration isnt dependant on the mechanical considerations with regards to valve spring although this has been largely negated by pneumatic valve springs now. All good info and if it results in a better running more economical engine then that's great.
However at the end of the day what valve clearances you use depends ( within reason) as much on "feel" and whats best for mechanical considerations. I ran my bikes with .15 and .2 from early on and when I changed to this setting it surprised me that it actually did feel like it ran better ( I was sceptical) however I also noted the starting was a little worse. Not to worry a couple of thou from factory settings isn't going to worry me mechanically and I traded one thing (starting) for a greater gain in the way the engine ran.
I'm not entirely sure I'd want to go to .25mm clearances though, just for mechanical reasons. That's .006" and .004" over the factory settings.I would be interested to see an engine thats used these clearances for 50,000 klms and see if there has been any mechanical considerations. It may have less wear,dont know. It also retards the effective valve timing fractionally which could be a good thing or not depending on how far away from spec it is due to assembly tolerances and cam chain wear etc and shortens the duration which probably isn't a benefit.
If Guzzidiag was around at the time and I'd fiddled with the mapping I could have probably made the starting better. Play with the settings and see what the current engine setup likes.
Ciao