when to enter submitted in mysql?

Hi to all! I have form made on 4 pages (by groups of questions). Right now my code works this way: once somebody submit the first page of the form his/her submitted info is entered in database with status=temp. I store the ID (insert_id()) in session and then every time visitor submit the next page I do update of the current record using ID. But, I heard once that "the best" solution is store all entered info in session (array) and insert all info at once. Or, instead in sessions, move submitted info with serialized array. Opinions? Thanks for help. -afan