I once watched a five year old child, in a school I worked at, die right in front of our eyes after swallowing a whole grape. EMS was called right away, and four adults did the Heimlich, multiple times, correctly. Sometimes it doesn't work. She died while we were waiting for EMS.
She was old enough and mature enough to chew. But sometimes things just go down. It happens, when kids are talking with their mouths full, or laughing, or just not being particularly attentive. It even happens when you're sitting right next to them.
I cut anything that's of a size to become lodged-- grapes, small tomatoes, cherries, hot dog chunks, etc. I cut them even for DD1, who's 5. We don't eat candy, but if we did, I'd cut that, too. I believe in the recommendation to do so until age 6, because it happens all too often. I have a friend who's an ER nurse, and she is constantly reminding me of this, because she's seen too many kids die, or suffer irreversible damage due to lack of oxygen, because of the Heimlich failing in small children.
I don't fuss about stuff like popcorn, sharp chips, etc., because even if those become lodged, they're not a size and shape to completely block the airway.