One of the interesting things about the new doc on the standard cell libraries is the reminder that the factory standard cells allow for the bodies of transistors to be biased. Here is an influential article from 2003 on why you might want to do that: Forward Body Bias for Microprocessors in 130-nm Technology Generation and Beyond. This paper shows how to get high performance from adaptive body biasing: https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.119.7854&rep=rep1&type=pdf There are also quite a few analog circuits that can take advantage of this, e.g. this opamp: http://www.saujs.sakarya.edu.tr/en/download/article-file/1069573