[julienkervizic]

Yeah, knowledge of window functions allows to solve quite complex data manipulation problems fairly easily.

For some data-engineering type of work such as sessionization, doing it without window functions would make the task really complicated.

In some platforms such as MySQL there are alternatives such as correlated subqueries that also allow to do extensive data manipulation easily, but at quite the cost penalty.

In my experience, people who know window functions, are already quite well versed in SQL and thus can serve as a good proxy to gauge overall experience in Analytical SQL.