Why create a police rule + a DNAT (PAT) rule

Good morning all

I ask myself the question of the interest of the creation of a firewall rule when creating a DNAT rule (PAT).

After my migration from 17.5 to 18, the import of my rules went well.
I then needed to access an equipment from the outside with a port translation (2222 to 22)
By default I wanted to use the DNAT assistant. (bad idea )

I then found some explanation on the net.

I saw that it was necessary to create a firewall rule then a NAT rule.
It worked.
To test, I deactivated the firewall rule and strangely enough I still had access to my equipment.
Do you have any idea why this is?

thank you in advance