In order to ensure users add the relevant department, class and location for every transaction and record, you could set the same as mandatory in Accounting preferences [Accounting Preferences → General → Classifications].
If you enable the preference to make the classifications required and use a custom form to display the classification at both the header and line level, the selection is required at both the header and line level.
If you wish to save Journals with no classification inputted at the line level, you may consider enabling the accounting preference ‘Allow Empty Classifications on Journals’.