Yeah, this feels like "premature optimization". When you design your applications and databases, it should reflect your understanding of the problem and how you solved it as best as possible. Using DATETIMEOFFSET NULL when you actually mean BIT NOT NULL isn't saying what you mean. If you already understand that you have a boolean option and you think you might need a timestamp to track it, use 2 columns. Or an audit table. So sayeth the holy SRP.