If the cut is not straight and the edges do not fit together easily, or if they are on a joint or somewhere that will open up with movement, it's worth getting it stitched. Also you want to make sure there is nothing in the wound - if there is, it needs opening up and cleaning and then you probably will need stitches.
If the wound is deep too you need to get advice because if you allow a deep wound to heal over the top, with bacteria in it, it can collapse and you end up with (a) a bloody great septic infection and (b) a shrunken pink scar patch which will not only hurt for ages but look nasty. I speak from experience. I had an exploding foot for six months that had to be packed daily with iodine soaked bandages.