If the piece of work is academic, then explaining why it matters is very important. I was always grateful to a teaching assistant who taught me to begin my assignments with a statement of what I was about to say and why it was important. I had a formula I could use for every paper I wrote. I'm sure it made a difference to my grades.
On the other hand, if the piece of work is artistic, like a novel or a poem, pointing out why it matters is counterproductive.
There should be a take-away point, an answer to the so-what question, but in most cases it should not be stated. Some stories for very young children will give such statements, but most other artistic works should not.
