The registration in Warframe Builder is free and optional. You can use the app without creating a user account. Creating a user account gives you the ability to save your creations and submit them to the community. You can also vote on designs submitted by other users. You can update and/or delete all of your informations at any time. If you change your password, the autologin cookie will no longer work. You'll need to login and check the box 'Remember me' again.