what is the practical implementation of using cisco tunneling (GRE ) ,why I should look for GRE nad there is VPN ?!

I use GRE tunnels for backups to my MPLS in each location. There are IPSEC VPN's with GRE tunnels back to central locations, with GRE you can pass BGP traffic.

With GRE you can route protocols that you can't route through the internet and if you have static wan ip or just one static wan ip you can use gre for free.