Rails脚手架方法的最佳实践

I am new to rails framework. I am confused that what is the benefit of generating scaffold instead of creating tables and columns in DB manually.What is the best for creating rich relational databases in Rails? And can I do bit advance things using scaffold i.e: changing the name of table and column after creating it. Restricting some fields to be private (scaffold should not generate a field in view for that particular private field)I am new to rails framework. I am confused that