The flower press will allow you to construct organic materials. Some are useful and some not so much. The most useful thing you can build in a flower press is land. So rather than having to use rafts to cover the water between areas, you can fill it with proper dirt.
Along with land, you can also create ore and some random organic stuff. Nothing that you can’t easily find out in the wild anyway.
Is flower press worth it?
Early on in the game, the flower press has little to no value. It doesn’t give you anything you need for survival. There are plenty more important things to spend resources on. Later on in the game, you may also have no need for it. Read over the items that it produces and decide whether or not you will need to actually build one.