These four functions are the complete toolkit for row-to-row comparisons and boundary analysis. Financial analysts use FIRST_VALUE to compare current stock prices to the day's opening price, LAST_VALUE for closing comparisons, LAG for previous-day changes, and LEAD for next-day predictions. E-commerce sites use FIRST_VALUE to show "vs first purchase" metrics, LAST_VALUE for "vs latest order" comparisons. Netflix uses these functions to compare viewing patterns: current episode vs first episode watched, next episode predictions, and series completion analysis. They eliminate complex self-joins and make comparative analytics simple.