I do agree in part.
If you are asking the motor to compress air at a higher pressure, you have to give proportionally more fuel to achieve any gain, otherwise you lose out to pumping losses.
Bear in mind that diesel exhaust flow, and thus boost pressure are entirely fuel dependant, more fuel = more flow. Run the motor at part load and you only get part of the full boost pressure, you don't run at max boost until there is enough exhaust flow to spool the turbo up to speed.
The thing to watch with non intercooled systems is that the exhaust gas temperature (EGT) can increase pretty quickly and cause damage to down stream compenents - exhaust valves, turbine wheel and bearings, turbo mounting fixings, etc.
In answer to why run 20Psi - 'cos it was bloody good fun
Jim