Because expense accounts are generated entirely by you, there are no statements against which you would reconcile your data. Therefore, there is technically nothing to reconcile. You can, of course use the reconcile process for expense accounts, which will lock the transactions for future editing.
One point to consider is that as your use of
GnuCash continues, the balances in these accounts will
grow, since there are usually very few credit transactions that reduce the balances. There is
nothing wrong with this situation, but some users may wish to clear the balances in their
expense accounts periodically. Zeroing transactions can be entered that transfer the balance
of the account to an Equity account.
GnuCash includes a Closing Books procedure that includes
zeroing out expense accounts. Keep in mind that this is not necessary, and that if you need to
gather information on a given expense account, you can use various reports to extract that
data without zeroing the account out.