Why Alias Block Lists if there is a Default deny rule on WAN interface

[salvador fx]

If there are block lists, tutorials,... it's because they are useful.
But despite being new to Firewalls:
What use is it if there is already a predefined WAN rule that blocks everything except what we created as an exception?
Firewall consumes more resources, such as RAM,... getting heavier, and maybe not having the strength left to stop a DOS, etc,...