I think this also depends on the field type. For example, with a Number field, you can store a text value, and FileMaker ignores the alpha and only processes the numerics. I have some tables where my SerialNumber field is a Number, but stored with a prefix indicating the table name, e.g.
Table: Customers Field:Serial Number AutoEnter Serial, starting value "cu0000001", autoincrement
Also, I just ran into a potetial "gotcha" where FileMaker would accept an "invalid" date during data entry, parse as as a valid date in all FileMaker situations, but then export it using the original (invalid) date format to an external service. See Partially Valid Dates - #2 by xochi
I'm intrigured by this idea that empty string (''") is not the same as NULL in FileMaker. Are there situations where this matters?