Internal-programming causes the Airbus LPC (Less Paper Cockpit) program, as far as Flap setting goes when OPTIMUM is left as the default, to choose the Flap setting that allows the maximum aircraft weight to be lifted off the runway.
For example, say the actual aircraft weight for takeoff is only 175T. The LPC program will calculate what Flap setting could lift 230T (or perhaps even more) and use the Flap setting for that 230T figure (disregarding the fact that the actual weight plugged into the laptop is much less).
What some pilots will then do, is go into the program and play around with the Flap setting to see if they can get a greater Flex (and use less thrust).
Why they do that, I don't know. Generally not wise, unless choosing a greater Flap setting for other reasons, such as tail clearance to avoid a tailstrike (FCTM contains text guidance that tail clearance is increased with a greater Flap setting - but tailstrike is really not a problem if SOPs are followed, anyway).
Playing with LPC flap settings is against FCOM SOP guidance (at a number of companies) is likely of little benefit (as far as we pilots are concerned) because pilots do not get paid extra for doing additional calculations with different flap settings. In fact, they may actually be punished for playing around with the Flap setting in the LPC... if they make a calculation or other mistake as a result.
If it ain't broke, don't
with it. Safer for the career.