It's mostly to use accounts for your business(es) versus your personal account.
For example, employees may use an official company account (e.g., GoDaddy) to do their job, but they also have a personal account for themselves (e.g., James).
It's also great for us moderators to easily switch between our personal account and moderator account.
Our fraud detection systems are very good to catch sellers bidding on their own auctions, so this feature won't impact that.