Why does “1” in awk print the current line?

Question

In this answer,

awk \'$2==\"no\"{$3=\"N/A\"}1\' file

was accepted. Note the 1 at the end of the AWK script. In the comments,

Answer 1

The documentation says

In an awk rule, either the pattern or the action can be omitted, but not both. If the pattern is omitted, then the action is performed for every input line. If the action is omitted, the default action is to print all lines that match the pattern.

So, it treats 1 as pattern with no action. The default action is to print the line.

Even if you have a couple of rules, like in

awk '
    in_net {
        if (/^\s+bindIp:/) {
            print "  bindIp: 0.0.0.0"
            next
        } else if (/^\s*(#.*)?$/) {
            in_net = 0
        }
    }
    /^net:/ {
        in_net = 1
    }
    1
' /etc/mongod.conf

You still need 1, since default action is triggered only when encountering rule with no action.