Rx is very general so it has unlimited utility, just like IEnumerable/IEnumerator has unlimited utility. IE pulls values, IO pushes values.
Foreach is a concrete example of where IEnumerables come in handy, but that doesn't explain IEnumerable, or yield or anything. Same goes with Rx.
Being able to look at something from either a pull point of view, or a push point of view, and being able to control the direction or means, is very powerful, because now you can push and pull computations around at will, using LINQ query operators for "free", against an IO, because it's the mathematical dual of IE.