Do firewall rules have to be symmetric? That is, does a firewall have to block a particular traffic type both inbound and outbound

Do firewall rules have to be symmetric? That is, does a firewall have to block a particular traffic type both inbound (to the protected site) and outbound (from the site)? Why or why not?

I have to answer the above question. What is the meaning of symmetric rules in firewall? can anyone please explain it to me