Pieces that add up to the original
When the width or height cannot be divided evenly, the leftover pixels are spread across the pieces instead of being dropped or piled into the last one. Neighboring tiles differ by one pixel at most, and put back together the pieces cover the original exactly, without a missing line or an overlap.
With a fixed tile size, for example 512 × 512 pixels for textures or print sheets, every piece has that size except the last column and row, which hold whatever is left of the picture.
Clear file names
Each piece is named after the original file with its row and column, such as photo_r1_c2.jpg for the first row, second column. Sorting by name keeps them in reading order, which helps when you assemble them in a layout program, a print shop or a game engine.
JPG, PNG and WebP keep their format and transparency. HEIC and AVIF photos are saved as JPG, GIF and BMP files as PNG.
What people split images for
Large posters printed on several A4 sheets, puzzle pieces for a classroom, sprite sheets and map tiles, slides for a social media carousel or a picture spread over a profile grid. For Instagram there is a dedicated page that also crops the picture to the right shape and numbers the files in posting order.