If we manage our database manually like if you need to add a column, You directly alter the MySQL database table and add the column.
If you need to add a new table into you MySQL database you directly create a new table.
But here is the question, If you are a number of developers and working on same project how will you get to know that who changed what in your database ?
If right now you are working on second or third version of app, How will you know what was your schema when you launched first version of your application? ...