In a number if builds that I have been playing with I find myself with Seismic Slam being my ONLY fury spender. At the same time I often find myself with A LOT of fury generators.
Here's a quick example: http://us.battle.net/d3/en/calculator/barbarian#beXYkR!Yed!YccbYb
So in this example Cleave would be the main source of AOE damage - this is obviously not a lot of AOE so it is paired with plenty of mobility ( Leap ), CC ( Ground Stomp ), and defense ( War Cry and Ignore Pain ). If you wanted to burn large packs of mobs down faster you could easily sub out one of those abilities for Revenge or Overpower or WW or something...
Anywho - the point here is that in this build Seismic Slam is the main source of single target dps. Fury shouldn't be an issue with so many generators, so maximizing the damage of each Seismic Slam is what counts.
On the other end of things we can imagine plenty of builds ( I wont bother to make one again.. ) in which Seismic Slam plays the role of CC - or CC with a bit of AOE dps. For CC you would likely want each Siesmic Slam to cost less fury thus freeing up resources for other DPS abilities. For a mix of CC and AOE you might want something like the Shattered Ground rune to get some extra dps and knock back at the same time.
It all depends on what type of play style you have and which abilities you plan on pairing together - Seismic Slam, like lots of abilities in D3, can fill many roles depending on how you want to use it. This, thankfully, allows players the flexibility to create builds centered around the abilities they enjoy using.
So excited for Tuesday...