Usefulness of PEX Manifold
implicit is also the fact that using the manifold results in less hidden fittings. That is, it's a straight run ("homerun") from the manifold to the point of use - no hidden tees, etc. There are advantages and disadvantages. The following document is a great overview of options for installing pex:

https://www.huduser.gov/portal/publications/pex_design_guide.pdf