The idea of IRM mini is to make a higher dpi version of the WS2812 matrix, from mostly 8mm pitch to only 4mm. And, to make it more easier to extend, we make 4 sides solder pads on it, to easily and neatly expand it as your wish.
Details
Easy extension
Solder pads on 4 sides, with both IN and OUT, makes it easy to extend IRM mini into a larger piece of display, whether with wires or just solder them together, it's your choice.