Disposable Email is used to kill spam. In reality, by using a disposable email in most of the subscribing forms, you prevent yourself from appearing on spam-lists, you fight against spam, and wild spammers
Or, you talk with a girl (or boy) on a chat, she (he) asks you for your email address, but you don't feel it very well. Let's have a visit onto Disposable email, and give her/him the generated address. You'll get her mail, but once the delay is over, you won't be annoyed anymore
Of course, you can use it in forums, in newsgroups etc.. There are so much ways to use it that it would be boring to list them all
Others way of use
Hide yourself to dredge your ex-. Preserve you spare time to read interessting emails, no more spam !. And why not, to say to your boss what you think about her/him... And no, Disposable doesn't cook, and isn't used to do the housework....