The ability to respond greatly to the faintest of incoming signals are crucial in cellular signaling systems within this complex molecular milieu. Sometimes to induce wholesale changes in the cell receiving the signal, tipping the balance between life and death, or between quiescence and a round of cell division just need one or at least a few input molecules (such as of a hormone). Signal amplification is the ability to amplify an incoming signal. The ability to amplify signal is even more amazing when one consider how the system need to be both resistant to many sorts of background noise (such as the random fluctuations in the conformation), its' activity, and local concentration of cellular components as they hustle about in the cell.
Then there is signal integration; a typical cell is simultaneously subjected to variety of different inputs, and often the response depends not just one but many type of signals. Cellular information processing is much more complicated than the simple conversion of one kind of input into another kind of