Okay, let me clarify, this is the rationale, not my defense of the move. Just want to clarify before people start thinking I’ve gone off the deep end like the original guy(s) who posted the idea on this site.
1) It is supposed to allow you to hold the Atlantic Ocean there by stopping England and America from sending any meaningful reinforcements to Russia
2) It is supposed to allow you to hold the defensive ground forcing the allies into over committing with warship purchases, against, stopping England and America from sending any meaningful reinforcements to Russia
3) It is supposed to allow you to set up Canadian Shield in a more subtle manner, thus allowing you to take E. USA or London before taking Russia. (I added the ‘or London’ because sometimes people worry more about Canadian Shield and not reinforcing England, etc.)
4) It can make staging Operation Sea Lion easier/safer.
Now, note, that not ALL four are expected too happen, those are just the four rationales I, personally, have heard for the move. I have attempted the Complex twice, and lost both games. Though, one of the games was at the hands of a deft master, the other was to a tottering, drooling, idiot (my impression of him, no offense to idiots was intended.) Note, the idiot is NOT A POSTER ON THIS SITE (caveat I have to mention so a certain somebody does not think I am referring to him. It’s a player I met at Northern Illinois University and, while he’s cute and has a great personality, I wouldn’t trust him to make tactical decisions on where to get my car serviced, let alone how to run my armies. Yet, he was still able to win with the German Round 1 Complex build.)