Freestyle charts exist for when something completely breaks a level, but when it's still possible for players to compete under the revised mechanics that have become the "best path". There's a difference between 7, 8, and 15 seconds in Cannon's Core that can be controlled by skill, and the ability to do such things deserves to be worth a mention.
There are other mechanics that not only break levels, they put an end to competition when they're used. Pause-B in the Genesis games, for example, makes it trivial to get 0:00 in any level, so it's disallowed. Pause-cancellation in SA2 is another good example: if you pause on mission 2 at the exact time when you collect ring #100, then select Restart from the pause menu, you'll be credited with level complete as soon as you restart. This would be a Freestyle-class trick and might be listed there except for one big problem: the timer just counts up as soon as you restart, with nothing further for you to control, and it saves your record as 0:08.25, every time you pull it off. There's no factor of "I did it slightly imperfectly so I end up with 0:08.27 or 0:10"; if you pull it off at all, you get exactly 8.25 no matter what. This leaves nothing to compete over.