[Panser]

'Tis a good question, and for a definite answer on whether or not it affects in-game performance I think you'd need to ask one of the "supermod" devs.

I'll say one thing I can definitely answer though - If you're cruising around with your scopes fully raised, you will be a whole lot more noticeable to the enemy.

I think in the real world it would also be heavily discouraged as keeping one or both scopes fully raised would raise the centre of gravity of the boat. This would effectively act as an inverted pendulum stuck on the top of the boat and make it roll a lot more in a heavy seas. I should imagine this could likely damage the periscope(s) by bending or twisting them if the sea was rough enough or they were kept fully extended for excessive periods of time.