intenal table with out headerline

hi,

i have a doubt,please clarify.

data:itab like <databse table> occurs 0 with header line.

or

data:itab like <databse table>occurs 0,

wa like line type of itab.

in above two cases , in my view no difference.

in first case there will be one workarea will be created with same name itab,

in second case we are explicitly creating work area.

ok.

here my doubt is in what cases it is madatory to create internal table with explicitly work area?

thanks in advance.

venu