Think about the target area and think in the sparring/fighting dimension. Not in the classic board breaking dimension. All of his kicks were mid-height, torso level. The angular motion would be negligible in terms of diminishing effectiveness. It has a Lot to do with how he is making power. He is penetrating And has some upward motion. The would potentially be more effective or painful for the recipient.
I agree with
@paitingman that it is another kick in the tool bag. For example, if a person is knee checking a lot or hands low or fighting very closed stance, putting the knee into the kick to get higher sooner makes sense. Or, if they are always on the aggressive using the 'sweeping' or 'upward' side kick is a better, quicker choice.
You have to measure time as a Big factor in your kicking choices. When kicking a target or board time in not a large factor. When the target is dynamic and ever changing time is a major factor so your kick has to accommodate the time issue.