For a couple of reasons that I can think of. You might want to do a rollback. You may have multiple copies of the database (various dev versions, staging, produ

For a couple of reasons that I can think of. You might want to do a rollback. You may have multiple copies of the database (various dev versions, staging, production), and multiple changesets might build up in one environment before progressing to another which must be specifically ordered. There may be changes that need to be manually coded or tweaked, and you need some intermediate structure for that to happen.