Using the same password for multiple accounts could expose all your accounts following a single security breach. Be sure to use complex and unique passwords for each account.
If you use the same password for multiple accounts, you increase your overall risk. The breach of a single account could potentially lead to the breach of all your accounts, because when a hacker knows your username (or email) and password on one service, he or she will try the same login information on other services.
Instead, use unique passwords for every account you have and change them often. Email addresses, personal banking, web services, mobile devices, and work computers should all have separate passwords.