Worked with the pre infusion presets today. I tested 0, 2 and 4 seconds of pre infusion with 16gr of coffee. I was using the Cuvee Meritage blend that I recently received (
see the Meritage thread on HB). I ground the shots for a 25 second pour. Not much change in grind across all three steps.
There wasn't a noticeable change in taste across the three settings. I have found as with my other machine that pre infusion does improve the consistency of the pour. You can see how deep two and four seconds saturates the puck from the following picture - not too far at all.

My take on pre infusion for the Dalla Corte is crank it up to four seconds (it won't hurt) and if you have a grinder that's not totally consistent then you'll see some improvement in the consistency of your shots.
Cheers
Ian