"A faction with two healthy players, MrApe and MrCow, had a faction named SuperAnimals. The faction SuperAnimals had 20 power. This was because the members had 10 power each and 10+10 is 20. They claimed as much territory as they could (20 minecraft chunks that is). Then MrApe went and drowned in lava. As MrApe died he lost 2 power. After that he had only 8 / 10 power and the faction SuperAnimals had 18 power as 8 + 10 = 18. At this time SuperAnimals had more land than they could handle (20/18). Then their enemy Bulldozer took the chance to claim some of their land. He managed to claim 2 chunks at the border of their territory. Then he could not claim more as SuperAnimals now had (18/18) land."
So if some of matts players lost power another player could take advantage of that and take it x
Edit: More info here
http://massivecraft.com/plugins/factions