By usage I disagree; I think most usage is rich content. Even news sites refresh their advertisements. (Of course, today they do a lot others, but I'm mentioning a case that most should agree is justified)
Even if I take that as an argument it is relevant during the initial load, while fetching the assets. (Also mind: reduce number of assets, improve caching of assets etc.) But for that the connection doesn't have to be kept up longer. For the next click it's almost neglectable.
Now we've gone in a circle. Because as was already said, if you're holding a connection open in case of future loads, the most private way is to always keep it open for the same amount of time.
