is it underattenuated/what was you SG and what is the gravity now? what yeast was it.
by underpitching the yeast had to grow more, and if you get too much growth you can get some off flavors and won't have the most healthy yeast.
All in though, pitching yeast in stages doesn't really work, unless its a higher attenuating one after a lower attenuating one to try and bring the FG down. they yeast reproduce to a concentration needed to consume the sugars in the solution they are in. less original yeast means more growth, and the potential off flavors, sluggish fermentation, and potentially higher FG.