what is purposes of Assign BSV at ledger level and L.E Level

Hi Oracle Gurus,

I have 2 questions related to Balance segment Value

Q1) What is purposes of Assign Balance segment Value at Legal Level and L.E Level in R12

Q2)

a) I have two ledgers and two L.E ABC Ledger, XYZ Ledger and ABC L.E and XYZ L.E

b) I have Company Segment  Value 123,124,125,126 and I have assigned Company value  123,124,125 to my  ABC L.E and ABC Ledger

c) Company Segment 126 not assigned to  ABC L.E and ABC L.E

d)126 company value assigned to XYZ L.E and XYZ Ledger

e) Same COA, same Calender but Currency are different.