User data is radioactive.

Powerful, but dangerous.

Requires careful handling to not mess up.

When you take on someone's data, you take on responsibility for caring for it properly.

In many cases, developers would prefer to not have their users' data.

But there isn't a good way to do this in the same-origin paradigm.

The one exception where developers will want it: if they are trying to build a data moat.

Users upload their data to that system, and since data is hard to port out, they stick to that service more tightly.

A dangerous bargain!