Why may it be better to use a high-profile cavity drainage membrane on the floor of the cellar?

If there is the risk of a higher level of water ingress into the basement, when refurbishing/waterproofing the area, it is wise to specify a high-profile membrane for the floor slab, such as Oldroyd Xv 20 which has a 20mm stud depth.(http://www.cellars.co.uk/products/basement-drainage-oldroyd-xv20).

A good example of a typical application for Oldroyd Xv20 membrane can be found via the following link: http://www.safeguardeurope.com/case_studies/basement-waterproofing-retail.php