You know the dreaded, ‘yes, but?’
Once we posit that the value of our lives is usefulness, we must confront the question, ‘whose definition of usefulness.’
I suggest this because the Baptist culture I grew up with (Southern Baptist with links to Calvinist thought) created a fractured view of usefulness. Too many parents continuously browbeat children because they weren’t doing anything useful, which meant vocations or pursuits of value to them. (This includes secular art, writing, dance and music.)
At the same time they pursued ‘useful’ tasks which intruded into others’ lives with gifts and gestures useful only to themselves. (Making sure you were on the right path to righteousness being one of them).
So, yes, I agree that we should pursue the task of usefulness but always with the caveats that this is a pursuit we demand only of ourselves and that we reflect on how we can most be useful, which may have little to do with employment, or making money, or fulfilling social roles. But neither should we forget that everything we do affects the lives of others.
The question I ask myself is, what will I leave behind that will 1) improve the loves of others and 2) be something they recognize as a benefit should they take the gift? Whether or not they choose to enjoy those benefits is up to them.