Let’s assume we have a game where rush files play against each other and ignoring the sp loss from SS effects and unit resurrection, we get a chart for the net sp bank that resembles the following. Where we have:
T3 – Tidal
T7 - Return
T12 – Wrath
T15 - Return
T17 – SS removal of a lvl 5
From this it becomes apparent, that the impact of removals is significant on the sp banks of both players. The idea of wk is to use the remaining sp in a more efficient manner than the opponent and eventually leading to a victory.
N.B. The idea here is not sp drain, but to create a low sp environment for both players and to use highly sp efficient WK units.
Sunbun brings up a VERY important point here worth discussion, although I disagree with him slightly on it. I wouldn't say that WK units are actually SP effecient considering they're completely average stat wise. I'm not really sure what sp-effecient means, but I think there is a slightly different thing going on here. Falkow units are designed to strike first, and strike in targeted spots. In low SP environments, that's actually really important. If you have a 1v1 or a 2v2 and you can attack first and hit specific units you can win combat that turn. So I don't think sp effecient is the right term, but rather that in low SP environments, being fast and accurate are optimal traits.
Another thing here is the concept of what low/high SP environments and how it relates to files. Some files can thrive in low SP environments. What I always think of is Lawtia Undead. Undead don't require SP to revive and return copies for 0SP, as such really don't need that much loose SP to thrive. Undead can get away with really heavy SP drain in the form of shades or in the form of deaths embrace. Not many tribes can really match undead pound for pound in low SP environments. Conversely, a lot of Refess tribes thrive in high SP environments where there is lots of SP. Refess units tend to get stronger the more of them are out on the field (since every unit buffs each other). So the higher SP environment you get the better you'd expect Refess to be.
As one final note, the SP environment steadily increases as the game wears on. This is sort of one reason why weenie rushes like to end the game early (they thrive in low SP set ups) whereas big files like the game to drone on (they like high SP environments).
The next question is how you can manipulate the SP environment. Let's look at some example:Lowering the SP environment
Return - Both players lose 3SP
Death's Embrace - Both players lose 3SP
Removals and SP drain lower the opponent's SPRaising the SP environment
Miffyre - adding SP to both players
+ SP souls
SP generating units and grims