Why split an image
Splitting is the practical answer to a layout that expects several images where you have one. Instagram carousels and profile grids are the common case: a single wide photo cut into three or nine pieces reads as one picture on the profile page while still being posted as separate images.
It is also how large diagrams get printed on ordinary paper. Cut a poster into a 2×3 grid, print each tile at full size, and join them — far simpler than persuading a printer to tile the page for you.