It makes a big difference on the product's durability.
The illustration shows both a "lockstitch" and the double-needled, leatherworker's hand stitch, sometimes referred to as a "saddle stitch." The lockstitch is the common sewing machine answer to locking layers of fabric or leather together. The machine employs an under-deck mechanism -- either a "looper" or a "shuttle hook wheel" -- which traps the thread from the needle above, forms a loop or "chain" and binds the two layers of fabric, leather, etc. together.
The hand-stitch employed by leatherworkers (among others) employs two separate needles, instead of one, and each needle passes through each hole from opposite sides of the assembly, forming a matrix that doesn't bind the threads to each other, but binds the leather instead (if that sentence doesn't make your head hurt, nothing will...)