Beyond the important function of kinases in ATP metabolism, it turns out that kinases play an important part of signal transduction, i.e. the way cells decide what to do in response to a stimulus. Basically, kinases affect the function of other enzymes, which are frequently kinases themselves. A cascade of such kinases link kinases that sense the extracellular environment (such as receptor kinases) to transcription factors that are regulated by phophorylation. This would lead to the transcription of genes in response to signals. Other kinases alter the rate at which enzymatic reactions occur.
Two Eds, Edmond Fischer and Edwin Krebs, won Nobel Prizes for discovering the importance of kinases.
There are a few other known signaling cascades including protease cascades involved in programmed cell death.