It’s easier if you don’t have to use a query to insert the current time and date. This is particularly useful for “date created” and “date modified” columns. MySQL doesn’t let you do both at the same time for one table, but there are ways around it.
I used the second option, inserting a null into the column. I read somewhere that it’s sort of hacky, however it appears to be legitimate behavior as seen in below link.
http://dev.mysql.com/doc/refman/5.0/en/timestamp-initialization.html (Scroll to the bottom)
Personally, I prefer to insert a NOW() value instead of NULL since it’s more intuitive.