Hello Ketan,
Static nat is usually configured when you need to provide outside to inside reachability for a given host. For example, a web server in your DMZ that will be accessed from the internet.
The only application i have seen of Dynamic nat is when you have overlapping ip addresses. In that particular case, we had to translate a 192.168.0.0/24 network into another range of IPs.
Last, but not least, Overload allows you to translate multiple internal IPs into a single outside IP. Sometimes also called PAT. This is often used for providing internet access in a border router or firewall.
