About firewall logs it is WRONG to say:

$$ Logging network traffic, even if you are just logging metadata, will increase processor overhead on the firewall and will consume disk space.

$$ The logs will help to correlate what you have been seeing and can fill in missing pieces if there are messages that have been dropped.

$$ All firewalls will automatically log dropped messages, but they can often be directed to log drops.

$$ No matter what type of firewall, though, looking at firewall logs will be useful.