Cell clumps forming during cell culture affects the accuracy of cell counting and also hampers the efficiency of oxygen transport and nutrition diffusion leading to apoptosis and loss of productivity.
In such a situation, anti-clumping agent is used which may alter the cell surface charge that may lead to single cell suspension. The concentration of anti-clumping agent needs to be optimized by the users.
One reason cells clump is because DNA molecules are released when cells die in culture, and because DNA is large and negatively charged, cells stick to it and form clumps. DNAse I has been used to declump cells. I have used it with some good and some not so good results. One thing that works really well is a Miltenyi product, their Tyto Running Buffer solution really does prevent clumps - so much so that I use it when I thaw cord blood MNC preps that have been stored at -80oC for over 3 years and had very good recoveries. It's not cheap - over $1USD/mL, but well worth it.