We track EE benefit balances (e.g. FSA) by EE number (= a project number) in a fund that doesn't require projects. That means that an entry can be made with no EE number which makes reconciliations challenging. (BTW - we are a small employer, <50 EEs)
We use project numbers as sports to track athletic expenses. If we could require certain accounts to use a project number, we would save lots of time correcting for missing projects.