When importing data into AX there are times where you might want to have data that you to extra manipulation on after you bring it into AX but before you commit it to the actual table. This is where you can use an entity that you construct. There might be times where you have simple data tables like parameters that you an prepare well before importing so it might be safe enough to import straight into the database. In this case you can use a table entity. This is a quick walk through of setting up a table entity.
PS: You can find a follow-up post here for importing from a file.