Difference between SU01 ROLE and attribute ROLE in org.structure

HI,

In SU01 transaction ROLE tab employee role is assigned to the user.

In org. strucute attribute ROLE also contains the employee role.

what is the difference between ther two ?

we should mention employee role for the user in SUO1 and attribute ROLE both places to create shopping cart ?

please guide...points are alloted.

Thanks

mani