>Can someone explain to me why Nulls should not be allowed in a database regardless of what type of field it is? TIA

Many reasons. One example:
- You have a client app that enters contact information. You have required fields such as FName, LName and Phone which are the minimum info you want on a contact. Your client app is properly done to not allow entries without filling these three fields.

Do you rely entirely on the app or do you also protect the database entries? Of course you do the latter (you could receive infor from different sources including web-pages). You create a rule or set of rules to avoid entering blank data. Call me paranoid but in this case I don't allow nulls as a further precaution. NULL to me means -I don't know- what goes here. An entry of Name and Phone as "I don't know" is not valid in a contact table.