I got the 1200's on lock :> Maybe I'll rejoin the ladder just for this.

Stack advantage is like, when you meet your opponent you'll have three stacks of 100 vs him having say, six stacks of 50. In that situation you would most likely wreck him :)

Also tying in with that is making sure you reach key bottle-necks first, as well as securing the most efficient bonuses as quickly as possible. Sorry if I missed this being mentioned already!

Edit: When I expand I also take into account what I call "territory" (much like in the sense it is used in Rugby) When I meet my opponent, I always want that meeting point to be where it would give me say, 60% of the map income behind my lines (even if it's still under neutral control) that allows me to take those bonuses later, whilst defending that "territory" from my opponent. Players who start near the edges in 1v1 or Team vs Team games often fall foul of this I feel. (In FFAs it's less of an issue and sometimes you might want an edge start for more "safety")

Edited 11/5/2015 00:10:51

What is a "stack advantage" as it applies to expansion armies?

Having a larger stack on the border with your opponent.
To make an example, if you got some intel from your picks and know your enemy is nearby, you might want to start moving a big stack towards him as soon as you complete your first bonuses

Master Ryiro would you mind wiping my ass?