By cons, if you want to tile the floor of a 6x6m piece diagonally and with a joint 2mm, will move to the pro or make a wider seal release. Because on a diagonal of 8m, the error can be 4mm ... which will cause problems on the regularity of the joint width.
That said, you can easily measure the error of this laser by drawing a line with a mason rule, then placing the laser in the middle of the line; draw the ends of two perpendicular. If they match, your laser is more accurate than indicated specification. If you do not have a mason rule, see the perpendicular 4 times, until returning to the starting point, and measure the error in considering that the laser positioning on a path is never entirely accurate .