Thus have I heard:
Samatha Jhana is used to temporarily eliminate the defilements, and set up the perfect conditions for doing satipatthana.
Some people say you should first get some level of jhanic attainment and then switch to satipatthana. Eg: get to the first jhana, then start the real work of satipatthana.
Some say you just need Access Concentration, then switch to satipatthana.
Some say you just need Momentary Concentration, and pretty much blend samatha and satipatthana into a single practise.
Anyway, that's what I've been told by some monks and books.
saturated with joy,
you will put an end to suffering and stress.