If you look in db/schema.rb you will see something like:
create_table \"users\", :force => true do |t|
What does the :force => true
From the Rails docs:
:force
Set to true to drop the table before creating it. Defaults to false.
Basically, this helps ensure database integrity. If you're manually tooling around with your migrations, it's helpful to ensure that you're creating new tables from a clean slate, rather than risking naming conflicts that stem from tables that have been created on a one-off basis.