When I was in middle school I once walked into the garage before turning on the lights and stepped on a mouse . The mouse was still alive and ran off because I hadn ' t put my weight on that foot yet . Since then when I walk into a dark room I am worried there will be a wall of mice . Not sure how my brain created that image but I always have to remind myself that mice would not be coordinated enough to stand wall to wall floor to ceiling all facing the same direction without needing to move . And this is any dark room , not just a garage . The kitchen , bathroom , office at work , bedroom . Any room where there is limited light my mind will imagine a wall of mice . <| sep |> A few reasons , but the gist of it is efficiency . If you ' re playing against AI this doesn ' t really matter , but in multiplayer it could mean the difference between holding the line and getting crushed . Field Marshals can command an unlimited number of divisions , but they gain experience much more slowly than Generals do . The traits available to them also , consequently , are gained much more slowly and are of a different type than the ones Generals get . The ones Field Marshals get are overarching bonuses to general strategy 10 % unit width , better logistics , planning , etc . , while the Generals get ones to specialize for specific battlefields , tactics , or units tanks , reconnaissance , hills , jungles , etc . This is pretty much where the differences tend to end , though , so if you feel alright with commanding one large group , then have at it .