Mangle - action= route ? some explain please

hi all
i don’t see any details for this action in http://wiki.mikrotik.com/wiki/Manual:IP/Firewall/Mangle

You can set a gateway to which the packet will be sent. It ignores the routing table.

i know what’s that mean

i don’t know what’s the purpose of this?
i don’t know whats its the different between mark routing and route ?? !!!
in which cases we use this action?

upupup