The value from generate_series is not used for anything, it is only used to generate the listed number of rows. The actual value in the examples is only provide

The value from generate_series is not used for anything, it is only used to generate the listed number of rows. The actual value in the examples is only provided by random(). You can create random strings, or other data types, to use with scalar selects. I had never thought of using generate_series for inserting random data, but like you said for some tables it doesn't make sense to use purely random values.