Why? Because you might (or at least, I *do*) want to sort a user's subscriptions by the date they actually signed up for notifications. In my case I only use the event type of 'node' and I want to be able to sort a view of a user's subscribed-to nodes by when they actually subscribed to them. At the moment this data does not seem to be available at all, but a first step would be adding a column to the schema to store this.

What do you think? Potentially useful? Happy to supply a patch if you think it's a good idea.