Joann Lublin writes in the Wall Street Journal:

As directors face increased investor scrutiny and heavier workloads, four board seats now look like a lot. More companies are putting in place rules that limit how many other seats their directors can hold. Only 5% of directors at S&P 500 companies held four or more spots in 2015, down from about 27% in 2005, according to a Wall Street Journal analysis of data provided by MSCI ESG Research. And just five people occupied six or more board seats in 2015, down from 308 a decade earlier.