The Absorbent Sponge collects the ink between passes for colors that are not being used during printing. When the nozzles on a print head are not used they can dry up which causes them to clog. The ValueJet fires off or "spits" between passes into the sponges to prevent the nozzles from drying out when they are not being used. For example, if the print job had no black in it, then every pass the head will spit black ink into the sponge so that it does not dry out.
