Well I don't know if what I read is correct, but someone wrote with 2 lasers it shows you the area you are actually measuring. Whereas one laser only shows you one point obviously, not the entire area the gun is measuring. That's my interpretation at least.
With temp guns the laser is usually below what is actually taking the temp so if your taking a temp of something the reading isn't where the laser is but about an inch above depending on how far away your holding the gun.