I think you'd be surprised. It's kind of like your house. The only necessary things there are the bed and the ceiling. And yet life would be much more miserable without all the random stuff you probably store in various cupboards.
These days I think of it in terms of cost to benefit ratios. I've for instance spent countless hours on Reddit, and while I got some benefit from it it is clear that the overall cost was negative even if it is impossible to know the exact figures.
It's still unclear to me which parts of the Internet provide a good ratio.
I guess for most sites, the cost-benefit ratio is a function of the time spent, following a steep downward slope. When I spend 15 minutes on HN every workday, it provides me with interesting stories and insights. When I spend two hours, it ends up draining more energy than it replenishes.
