The idea of swapping is to reserve some storage where the kernel can place pages of memory that are not mapped to a file so that it can free up the memory for other uses. It increases the effective size of physical memory by the size of the swap file. It is not a panacea: there is a cost to copying pages to and from a swap file, which becomes apparent on a system that has too little real memory for the workload it is carrying and so swapping becomes the main activity. This is sometimes known as disk thrashing.
Swap is seldom used on embedded devices because it does not work well with flash storage, where constant writing would wear it out quickly. However, you may want to consider swapping to compressed RAM (zram).
