The latter. Useful means that it provides value that somehow improves the human condition. Everything from food to fuel to art to architecture is that. Random junk on the net is not.

A central fallacy of present-day economics is the assumption that all economic activity is of equal value. GDP is a good example: A million dollars spent on healthcare increases GDP by a million. A million dollars spent on war increases GDP by a million. A million dollars spent on rubber dog crap increases GDP by a million. But these transactions are not of equal value.

I personally think that economic central planners and GDP growth targets are a major underlying cause of all this useless make-work. I call it the gerbil wheel economy.

Run, gerbil, run! Gotta make the opaque meaningless numbers bigger!

You can see it very clearly in very centrally planned economies that worship GDP growth, like China. They have entire abandoned cities-- things built for nobody, just to make opaque numbers bigger.