It is recommended to seal concrete to protect it from salts and chemicals brought in by vehicles, but all sealers are not created equal.  A sealer used on the same day the concrete is poured is considered a cure/seal and is a very good option for retarding the evaporation of needed moisture during hydration but not a great option for the extended protection of the concrete.  I stand fairly firm in my opinion of “you get what you pay for”.  There are low-cost sealers that are more along the line of siliconized water and do not last very long under vehicle traffic.  Better sealers result in a thicker application and protect better and for a much longer time.  Sealers, other than the first one mentioned, require concrete to get to its designed strength which is typically 28 days prior to application and require a clean, dry surface.