Using Logged Voucher for Purchasing

Hi All, greetings. I have a Q about using logged vouchers for purchasing. If I would like to capture PO information on the logged voucher, I suppose I can use PO fields under "Form Exit > Additional Information". My Qs are:

1. Would "Form Exit > Additional Information" validate to check if that PO no/type/line# actually exists in F4301/F4311?

2. Would this PO info on logged voucher be available at the time of logged voucher redistribution to assist redistribution?

3. What is the main reason behind having the "Form Exit > Additional Information" PO fields', as in how do we expect to use them?