The higher they are, you have Information about the correct numbers and Type of Ships, Planes as well Army-Equipment. That´s the first thing.
You get Information about the active Generals, Admirals and Special Pilots. That´s the second thing.
Your Troops fight better with that Informations, because they know weaknesses and strenghes of the Enemy. (but it´s not confirmed yet from Players which test that). And much more, that I don´t have in Mind yet.
You can increase the % of Infromation you get with a Spy-Network and with Spy-Planes as well as the main important 4 Parts on the Top of your Agency and Infiltration of your Agents in Army, Navy, Airforce and Civil.
That all was comming with Patch 1.9 and DLC La Ressistance and will be constnatly improved with the next Patches and DLC´s.