I'm specifically referring to DIY.com here and I have not seen this type of navigation before (have you?)
My question(s) is(are) this: what are the reasons why www.DIY.com have hidden some of their sub-levels of Navigation behind "view alls" upon rollover of primary category eg. garden? What are the advantages and disadvantages of this UI? (ie. in this example, there are actually 6 sub-categories under "Sheds and Storage" but they've decided to only show 3. Why? Is there any research to support the advantages of this?
I can take a good guess as to why this is the case (reduce level of cognition, reduce choice, promote certain sub-categories). A clear disadvantage being summarised by Jared Spool.
Users can't predict the future, so they don't know they need to reveal the menu to get what they need. - Jared Spool
Here is a screenshot: