I have seen it before. I am just wondering what exactly does it do?
-f, --fix-broken Fix; attempt to correct a system with broken dependencies in place. This option, when used with install/remove, can omit any packages to permit APT to deduce a likely solution. If packages are specified, these have to completely correct the problem. The option is sometimes necessary when running APT for the first time; APT itself does not allow broken package dependencies to exist on a system. It is possible that a system's dependency structure can be so corrupt as to require manual intervention (which usually means using dselect(1) or dpkg --remove to eliminate some of the offending packages). Use of this option together with -m may produce an error in some situations. Configuration Item: APT::Get::Fix-Broken.
Here's where I found it very useful. I ran a dpkg command to install a couple of .deb packages, but the install failed because some dependencies were missing.
I then ran
apt-get -f install
and it installed exactly the dependencies that were needed. I was then able to re-run my dpkg command and everything worked.