You know your own phone number and email address, so why would you have an entry for yourself in your contacts? For Lifehacker reader Ben, the answer is that it's a handy place to keep other personal information.
As he explains:
I store myself as a contact in my address book. There I keep non-sensitive information such as work personnel numbers, or account numbers for other organisations. Funnily enough I find myself looking myself up in my address book quite often!
As Ben suggests, this might not be a good idea for more crucial data such as your tax file number or passport number, though if you've secured your phone with a password then there shouldn't be too much risk. I personally keep these kinds of details in a text file stored on my phone, but using contacts is a pretty elegant solution. Thanks Ben!