The aggregate with rounded shape has the minimum percentage of voids ranging from 32 to 33%. It gives minimum ratio of surface area to given volume and hence requires minimum water for lubrication. It gives good work-ability for the given amount of water and hence needs less cement for a given water cement ratio.
The only disadvantages is that the interlocking between its particles is less and hence the development of bond is poor. This is why rounded aggregate is not suitable for high strength concrete and for pavements subjected to tension.