Imagine a card game and development of the game program vs. running the game to actually play it.
Pseudo-random number generators use a seed or seeds to determine the starting point of the sequence. Some of them always make the same sequence, others can produce different sequences depending on the seed. Some use a cascade, a simple RNG is given a simple seed, and this is run for a while to produce a more complex seed for the masterpiece RNG.
It is quite useful to be able to deliberately repeat the sequence when developing the program or when one wishes to reproduce previous results.
However, imagine a card game. It's obviously not a good idea to always deal the same sequence of cards.