A common problem is that you want to be able to have access to your data, but you aren’t sure where you’re going to be at the time you want to access it. There are several different solutions to that. One is to carry all of your data around with you. In fact I do, it’s that laptop, chained down over there. But I don’t want to carry it absolutely everywhere, because it’s a bit heavy, it’s a nuisance, so in practice you want to use equipment at the location that you go to. On the other hand, if you do that then you’re revealing information about yourself: the data itself, and — if the system isn’t designed properly — you may also reveal authentication information that allows somebody else to masquerade as you later.