Hi David,
I see where you are coming from but the issue with that is that then if you need to search for records with missing data you won't have any and therefore a lot of your records will have bad data in them. It's better to have no data then bad data.
Yes you could search for "-" instead but that is just causing problems, what if it's a number or a date field.

Remember when searching you need to check for null or blank
Is Null or = "" (empty string)
Null being never having had a value or "" having a value then it being deleted.

Alex