Slime works to keep a tire from going flat out on a ride. Even with the thorn in the picture, I made it home without a flat. However, little thorns get in the tires quite frequently and when you pull one out, the hole starts oozing Slime and continues to do so until you patch the tube.
Slime, however, does spray out on your hands and rim when checking the air...and the stuff stinks, too.