I have blogged about the disadvantges of using integers instead of proper date or timestamp values.
Another (frequently ignored) advantage of using date or timestamp values, is the fact that it’s easier to do date arithmetics with them - especially when combined with the interval data type.
Recently I see an increase in questions in various forums (including Stackoverflow) where people are using (big) integer values instead of proper timestamp values to represent timestamps values (less so for DATE values though).
All modern databases systems provide highly efficient data types to store real timestamp values, but I often get questions asking what the actual downside of using a “UNIX epoch” instead of a proper timestamp is.