As you might have noticed, many web sites have recently been attacked and many passwords leaked. As soon as that happened, many bad guys tried to use those passwords on other sites to gain access to user accounts. Though we all know, that we should have a separate password for each account, it is hard to impossible to achieve this in practice. Human brains have not evolved to remember randomly generated / meaningless strings.
Of course, there are existing technical solutions, like file or cloud based password stores. Those encrypt the passwords you use with a master key. However, you always have to have the file with you, or, in case of cloud based systems, have to trust another instance.
Please be aware of the remaining risk that you could loose your master password, due to malware running in your browser or on your operating system.