Rebuild Sort Files (utility) is used to recalculate the OnSO/OnPO... values.  Click Yes to the prompt to recalculate (the specifics of which will be different for the different modules).

Do we need to rebuild both PO and Inventory?

IM recalculates committed lot/serial quantities.  PO recalculates the OnPO value.  I generally run through all the modules when I do this, to fix any issues that may exist.  Rebuild Sort Files is safe under most circumstances.

Hi Kevin,

Should we do the rebuilds in a specific order; IM before PO or viceversa?

Order doesn't matter.  Each one does different things.