According to its main readme file, Lenovo Nerve Sense is used to overclock the frequency of the supported Intel processors (the ones with K). It's not necessary to have the application opened at all times because it modifies the values, then it can be closed.
However, I would take extra precautions when modifying CPU values or anything else. Read carefully what your computer supports and what are its limits. You can usually find all the necessary information on how to tweak and overclock the performance of your device.
