Setting a different email address form sending Invoices to your Customers helps ensure any replies from your Customers are sent to the correct address.
For example, you may wish to use an email address starting with finance@, if you have a specific finance email address.
You can set your email address form sending Invoices to Customers in:
Setup > Organization > Invoicing > Invoice Email Address
Learn more about how to email Invoices to your Customers here