Another reason is added security. The joint registrar/hosting companies allow you to use the same account/password to access and update the site that you use to

Another reason is added security. The joint registrar/hosting companies allow you to use the same account/password to access and update the site that you use to transfer and register domains. My rule of thumb is the registrar, www hosting, email hosting and DNS all be totally separate and have unique accounts with different companies. They all use unique passwords too. A compromise of one will not compromise the others.