From my experience playing in the Principality Stadium, it makes a massive difference on game-day whether you have the roof open or closed.
The atmosphere is definitely that bit more intense when they close it. But not only that, I found it so hard to play in because it feels like you are actually playing at altitude.
The air is being shared by 80,000 people and then the ground can get a moisture on it as well, which makes the ball become slippery and the running surface that bit stickier and harder to judge.
Overall, it can be really energy-sapping. I just found it really draining on the system. And it will obviously favour the home side with the majority of the support. Personally, I hated playing with the roof closed, particularly coming out after half-time, it was like coming back into a pub.
Any time I played there we wouldn't have agreed to the roof being closed. Both teams have to be in agreement obviously but I think it would be foolish to ask for it to be closed.
The Welsh would be more used to playing with the roof shut and everything like that matters when it comes to the top end of international rugby - why would you hand them that advantage on a Friday night in Cardiff?