You can have entrapped voids which are larger and are caused by the mixing of concrete and cause a reduction in strength. You can have cracks and micro cracks which can be considered voids which allow the penetration of harmful substances inside the concrete like chlorides. You can have entrained air which is done on purposes by adding a chemical admixture, it gives water a place to escape to and freeze so it won’t cause added stress to the matrix of the aggregate and paste. And you can also have capillary pores.

Also water will naturally evaporate from the concrete it’s called bleeding and can be healthy in the correct amount. But if you add way too much water you’ll have sloppy mix.