The difference between FUL and PER in PM Order settlement

Hi PM Guru,

There are many discussion on line surrounding FUL and PER but none of them is helpful to me in particular.

Usually in the settlement rule of PM order, both PER and FUL are maintained.

I tested OK that even though I only maintain FUL without PER, settlement is still done.

So, what is the difference between  PER + FUL and  only FUL in the settlement rule for order settlement?

Thank you so much,

Sally