IF YOU CREATE WITH HEADER LINE THEN YOU NEED NOT HAVE TO 
CREATE A WORK AREA EXPLICTLY.

IF YOU WANT TO CREATE A WORK AREA THEN TWITH HEADER LINE IS 
NOT AT ALL REQUIRED.

CHOICE IS YOURS.

in this question we can proceed like this.
with header  line.
data:itab like lfa1 occurs o with header line.
itab:internal table body.
with out header line:
data:begin of fs,
     field1 like lfa1-field1,
     end of fs.
these are syntaxes for both...but if u want to extract all
the fields from predefined table or exhisting table.. very
complex to write all field names in internal table
declaration.so that time use with header line syntax.

fields are very few..go for with out header
line..performance wise with out header line is better.