I do not agree with that statement. In lots of roles, it does not matter whether you answer now or in one hour, but being constantly disrupted unexpectedly can have a dramatic impact on concentration and productivity. I cannot do any substantial programming or data analysis if I expect to be disrupted. The problem is not someone calling because the house is on fire and I am the only one who can fix it; the problem is someone screaming for my attention to e.g. know if I will participate in an event in 2 months time. Avoiding unnecessary disruptions is not letting people have leisure time, it is allowing them to do their work properly.
On that topic I really like that piece: http://www.paulgraham.com/makersschedule.html