DBMS_LOB.COPY vs Variable Assignment

Hi,  Is there any difference between assigning the lob object directly (1 below) to a lob variable and by using dbms_lob.copy (2 below)  if i am copying the complete document?

 

Declare

a blob;

b blob;

Begin

 Select lob1 into a from xxt;

b := a; -- 1

dbms_lob.copy(b,a,dbms_lob.get_length(a)); -- 2

End;

 

Thanks,

Lakshmi.