Anyone who follows our thoughts will know we are not keen on hidden navigation on corporate sites. We believe this is a trend that has made life more difficult for users and the possible benefits - in terms of a 'cleaner' look - just don't compensate. Our conclusions come from our own extensive testing, but is always nice when a large scale study comes up with the same ideas. That is what Jakob Nielsen's lot have done, and they are well know for doing things thoroughly.
The result is summed up when they say 'Hidden navigation provides worse user experience than visible or partially visible navigation.' Another point that echoes our cries is 'Responsive design has many merits; however, one of its less fortunate effects has been an excessive popularity of mobile-first designs that translate poorly on to larger desktop screens'. This last is particularly relevant for corporate sites which, we know from our data, are mainly viewed on desktop or laptop computers.
Here is a piece I wrote explaining why corporate sites are like Brussel sprouts (there is a link, honest).