It all depends on your refinement level. It's a really high, high end form of increasing power, since it increases stats of ONLY 1 ITEM BY ONLY 1%. Lets say you have +450 ini/crit/injury/control/combo on an item and all yellow purification with 100%, then you have a total of 900 of each stat, Purification pill gives you additional 1% of total stats, so a whole whooping 9 of each (so propably, like 50 power at max).
Max level refine gives you 665 stat, so even with 100% purification its only 13 stats of each from a single pill.