It really seams like it's just a neat trick to make the sums easier.

Part of what's weird about fundamental physics is that it is, in a sense, all just tricks to make the math easier. When you get below the level of non-relativistic QM (and even, arguably, at that level), the distinction between the mathematics of the theory and the theory itself starts to collapse. Some of this is probably just due to the fact that events and patterns at that scale are just so unfamiliar to us and our everyday experience: we can make intuitive sense of things like forces, acceleration, mass, and other stuff that's in the ontology of classical mechanics because we live in that world. Fields, Lie groups, fiber bundles, and other essential bits of the formalism at the QFT level are much harder for us to understand, because they can only roughly be mapped onto things that are familiar from our lived experience. This is part of why things like QFT, QED, and other candidate "fundamental" theories just seem like bags of mathematical tricks: in a very literal sense, those theories are telling us that the world just is a set of formal relationships and interdependent patterns. When you ask something like "well what is the theory really telling us, beyond the math?" for classical mechanics, I can give you a story--a narrative--about the world that maps the mathematics onto familiar concepts. When you ask the same question about QFT, there's no easily accessible metaphor or story: it's structure all the way down. Statements like "light sometimes behaves like a particle" means nothing more or less than "it's useful to think of light as being quantized in some contexts, because the mathematics seems to work that way."