It mostly depends on which mod you are using.
In stock I don't think they are relevant at all.
TMO, Duci reworked the traffic layers quit a bit but I haven't noticed any
relevance to big battles unless the message so states.
RSRD has all the big battles and the messages will often point you to an area where something will happen, either a convoy or a battle.
But to find battles you really need to know your history.
Check out this site.
http://www.combinedfleet.com/battles
Magic