[Carpetsmoker]

You don't need anything, but it's a useful way to do it without any significant drawbacks. In many cases, it's more or less the only option.

[cpuguy83]

It is a significant drawback! It is literally not the only option to the situation you described.

Spying is the only solution for spying, yes. Spying is the only solution to over-eager people wanting mostly useless metrics.

It's not much different than me checking my Twitter "likes" constantly.