In teoria:

Backing up is something we all know we should do, but often don’t. And while disaster is a great motivator, now it doesn’t have to be. Because with Time Capsule, the nagging need to back up has been replaced by automatic, constant protection. And even better, it all happens wirelessly, saving everything important, including your sanity.

In pratica:

What causes their sudden death?

In one word: heat. Contrary to what Apple suggests by their magical “affected serial numbers list”, the serial numbers in the Time Capsule Memorial Register show that the problem that causes the Time Capsules to prematurely die is not limited to certain production batches. Experts on the subject, like LaPastenague, have confirmed that it is the flawed thermal design that causes Time Capsules to stop functioning, not the quality of the components used. All components, including the power supply, are squeezed together in a very small package with hardly any ventilation to cool them down (in fact, that rubber foot works as an insulator). There is a fan inside the Time Capsule, but it is totally inadequate (it will start only at extremely high temperatures, and will only circulate hot air). The first components that die from the prolongued exposure to high temperature are the capacitors in the power supply unit.