Does Time Machine take advantage of two backup disks to backup more fine-grained snapshots?
Time Machine will continue to perform hourly backups, rotating through your backup drives. Each drive will contain a full, independent backup of your source drive.

This provides redundancy for your backup system, if that is what you seek. In case one of your backup drives fails, you still have another. This can prove particularly useful if you keep one of those backups offsite (backing over the Internet will require special setup, however, and can prove agonizingly slow).

The ability to use multiple backup drives was introduced starting with OS X 10.8 (Mountain Lion).