SHA1 use cases are not limited into integrity verification of documents, but used a lot for traffic integrity and generation of authentication codes:

- Torrents of all kinds. - Version control systems (where ability attacks like displacing release pointers become easier). - IpSec, SSH, PGP and a number of other protected data exchange systems.

Being able to subvert integrity guarantees is a nice building block for complicated man-in-the-middle attacks.