Where do we need synchronization?

In the telecommunication network, we know for several networks needed synchronization to optimize that network performance. where do we need that?

1. Public Switched Telephone Netwroks,
2. SDH and SONET transport networks,
3. SDH/SONET over DWDM transport networks,
4. ATM networks,
5. Cellular mobile or 3G networks,
   
6. Digital broadcasting,
7. A.o.