All terminals (A-F) are connected by a main hallway/walkway.

Once you clear security at terminals A,B,C,D or E you can roam freely within the secure zone at any of those terminals.

While you can walk to F, indoors, there is a security checkpoint you have to go through again because it's set in further than the walkway ends. This is why most people will take the shuttle from C to F, because the shuttle drops you off in the terminal - behind the security checkpoint.