Randomness provides variance, which is essentially the range of opponent skill levels you can compete with. GoFish has high variance so anyone can play against anyone else (but is so random as to not be very fun) while chess has no variance so the better player almost always wins (also not fun, unless you match up well).

While unpopular with skill players, variance is handy in casual games like Catan because it broadens the range of people you can play with. Variance in the form of mana-screw in Magic does the same thing, with the bonus of allowing you to compete with a wider range of skill and money levels.