Hi, I've seen in several scripts the following layout:

iptables criteria -j ACCEPT
iptables the_same_criteria_as_above -j RETURN

for example:

iptables -A INPUT -p tcp -m tcp --dport 100 -j ACCEPT
iptables -A INPUT -p tcp -m tcp --dport 100 -j RETURN

The last rule will be never matched, because all tcp incoming
connections will be accepted, and then will go throw the next chain.
So, What is the usefulness of this configuration?

IMHO, I think is for changing the scripts in a fast way (just
commenting on the first line will yield in default policy for the
INPUT chain)