As the others have said the chaintool is sometimes needed for the removal of the damaged link so that you can then fit your "powerlink" in its place.
I can think of two examples.
My ONLY ever time when I called out the wife to rescue me in the car. While pulling off, I got my gear change slightly wrong and it put a tiny nick in an outer link. I could still ride but the kinked bit of chain jumped every time it was fed onto the rear cassette. So no chance of doing the 20 hilly miles that remained. I may have been able to sort it out but it was already near midnight and quite welcomed the easy way out.
Another time while lubing a chain in a lay-by on my way to an Audax in the car (hadnt completed the job at home) I noticed one of the outer links was cracked, quick removal with the chain tool, fit a spare split link and I can then start the Audax with a healthy chain.
So two examples in 53,000 miles which isnt enough to make a chain tool essential but enough to make it worthwhile, not to mention helping others out occasionally. I first got it when a friend's chain broke up in the hills off roading in "The Valleys" as we were doing the long walk some guy stopped, produced a Hexus and got us going again. We both went out and bought a Hexus each within a week.
A Hexus or similar tool means you always have an adequate chain tool with you and are never bothered by its presence.