After the concrete has been poured and cured, adding a sealer helps protect it from future damage, corrosion, and stains. Because concrete is porous, it tends to absorb water and other substances. Sealing closes pores and prevents any future freeze/thaw damage to the concrete which can result in cracks. In warmer climates like Phoenix, the freeze-thaw cycle isn’t a concern however it is still recommended that you seal your concrete to protect it from harmful chemicals and UV exposure that causes oxidation.