His pace and tireless work ethic is a needed quality on this team that doesn't always show up on the stats sheet.
That sequence was a microcosm of what he means to the club.
Notice that there were 5 Napoli players around him, and he outmaneuvered most, if not all of them in the 79th minute of a match that was taking the life out of nearly every other player on the pitch.
I know that a lot of people love to call him useless, but the bottom line is this.
You can't teach speed
You can't teach heart
You can't teach work ethic.
And regardless of what he does for the rest of the season, it is obvious that he has these three qualities which make him, for the moment, indispensible in Conte's system