Filter rule association: Associated filter rule VS Pass

[sirio81]

Hi all, if I redirect a port (Firewall / Nat / port forwarding) I have 3 choises.
In this topic I consider only two of them:

• Associated filter rule
• Pass

The first is the default.
It adds a rule in Firewall / Rule / Wan.
This rule can't be edit.
If I choose "Pass", no firewall rule will be checked.

I both cases, any request on the forwarded port will be accepted.
So, when is the case to prefeare "Associated filter rule" instead of "Pass"?