I saw many people write this command in their configuration and I have conflict with it. The command is
I know that we can write
to translate the inside IPs but why global (inside). Please clarify this.
Without a corresponding NAT statement as far as i know the global statement is doing nothing. Maybe just some left over config.
The use is more evident in a large network. If you don't use a default route pointing back to your internet gateway and you have multiple routers you would need to have routing entries in your routing tables for all possible addresses. Some people don't want that and they also don't want to use a default route so it makes sense to translate all source IP address coming in to a routable subnet on your network.
The reason you may not want to use a default route is security related. If an outside user can gain acccess to your LAN if you have a default route the return packets will automatically be routed back out to the internet. Without a default route the packets would get dropped within your network.
Obviously this is not your first line of defence but mistakes do happen and firewalls can be misconfigured.