You want the water in concrete to hydrate not evaporate. The sealer locks in the water so it does not evaporate. Thus giving you stronger concrete and less micro voids from evaporation.
That being said too much water will also weaken the concrete. People add more water to make the mix more workable.
Concrete by its nature is strong in compression and weaker in tension. This is why re-bar is added for tensile strength.
Not an expert but many years in construction.
Concrete mix is like the male member, the stiffer it is the better it works.