Focus
Productivity isn't about banning, it's about setting goals and sticking with them. If an employee has specific objectives to be met ... and meets them, who cares what else occurs during that employee's day? It's an old-manager-mindset: Ebenezer exacting specific hours of 'work', instead of looking at tasks as entities. The punch-clock mentality. So, you'll see people who *never* get on FB or check for messages on their phone or anything else and do the rock-bottom absolute minimum, but because they are "working", the boss is happy.
Needs a re-think, don't you reckon? Define your tasks and objectives first. The rest: who cares. Your objectives are met... does that other stuff even enter into the equation?