Nets are a hazard for skidded aircraft but in the N Sea everything has huge wheels these days. That said, there is a general move to get rid of nets in favour of high friction surfaces (ie paint with sand in it!) which is definitely better for my ankles.
To answer 13snoopy directly, they are to increase the friction between the wheels and the deck, esp for moving decks so that you don't slide on the deck. Probably also helps to stop you sliding off the edge when you make that unexpectedly OEI landing with lots of fwd speed.
In the good old days also used by passengers to claw their way across the deck in 80kt winds - now not allowed to fly in those conditions I am glad to say!
HC