Basically the main difference is the way that they decrease the particle size of a solid and its final particle size, usually the crushers  hold material between two parallel or tangent solid surfaces, and apply sufficient force to bring the surfaces together to generate enough energy within the material being crushed so it separates and cutters remove material by their movement within the machine or directly from the cutter's shape
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First you have to differentiate between crushers, shredders, cutters and mills 
Also the kind of solid matters, due to if its has water as fruits, you should not use a shredder, it can get damaged ,and if you want a powder as flour from grains, it would be better to use a mill
This is a complete science and possibilities are infinite, tell us wat you want to crush and we can suggest you which is the best way to do it
Thank youuu, i want to crush an edible fiber into powder, but i don't know if i should use a mill or a shedder
If you want to obtain a powder ypu should use a mill, a sheader give you sheeds, so in this example what matters  the most is the final particle size