The Metropolis release adds ADD and MUL operations on elliptic curve, which makes it possible to implement ring signatures.
That opens up use cases like anonymous funds transfer similar to Monero and zCash.
While interesting, privacy is not a switch you use when you really need it. It has to be always on, to protect everyone.
What do you mean?
You can only be anonymous by blending into a large anonymity set. If the very act of using the privacy features singles you out as being part of a small set that is trying to be covert then it makes things worse.
If you're the only one using Tor on a network, you can be easily singled out and identified.