Cost: $5 for a tube of concrete sealant.
Poured cement is certainly not the best insulation, but when its surface is compromised by cracks, it becomes even worse. Cold air and gases from the ground can pass through to the garage when a small crack is present. To make matters worse, if you are constantly introducing water into these cracks, such as after driving in a snow storm, the water can freeze and expand below the cement causing upheaval and shifting. If the concrete slab shifts too much, the floor will become uneven and this will compromise the ability for the garage door to completely seal in the closed position.