Don’t design the new sign up. Don’t design the new comments widget. Don’t design the new sharing widget. Don’t design the new image upload interface. Don’t design the new rich text editor, or a feedback tool — the list goes on and on…
Don’t start with 0 reviews of the products you sell. Don’t ask people to fill out a bio and upload an avatar from scratch.
All of these building blocks and information are out there, available for reuse and integration.
…unless one of those things is the the key value, core and heart of your business.