When entering a journal entry, I feel that when you enter a project ID that isn't allowed for that particular account number that it should alert you immediately instead of when you save or validate. When doing a large journal entry, it would be very cumbersome to try to find all the account numbers that you may have made a mistake on.
You have this option. You can set it in the User Options. These option settings are user specific so you would need to set them on all users.