the off set gives you an idea what your textre looks like when the eges meet, when one tile meets the next one, * saves you the time of make'n a PS file four times the size and putting 4 full size images next to eachother to see if there are Hard eges, one way to get the perfect tile you basicly offsett, clone, heal, or paint over the hard edges. offsett again, clone, heal, or paint .. and save.