Depends on where your shots were going with the closed club face. I used to have an awfully closed club face. As you say it was great for distance. But it got to the stage where I could no longer control where the ball would end up as I was hooking and hooking it more and more.
So I was told to open my grip to make the club face more neutral. Which I did. And now I have lost about 10 to 15 yards with each club and I have a nasty slice. 
To be honest I'd say if you are enjoying it, you are getting good distance and you are hitting a good percentage of fairways then don't worry too much about it. As the danger is you then spend time and effort trying to remodel a swing, but for what reward? Don't get too hung up on trying to have the perfect swing if the one you have works and you don't intend to be a pro.
But on the other hand if you are drawing a lot of balls vast distances into the rough with little consistency then listen to what the man says. Better to be 100 yards down the fairway than 120 in the rough.
