Chunners is not an orthodox fireball character. You aren’t going to win fireball wars with Kikoken, nor are you going to be able to zone as well with it. I think a lot of mid-level Chun’s make the mistake of trying to base their ground game around Kikoken, which is not the greatest of ideas.
As you all should know, naked Kikoken at just under 3/4ths screen is a bad idea. Most characters can easily jump over it on reaction and get a free jump-in combo - and this is a practice often employed by shotos. Even if Chun recovers, at best case you are forced to block the jump-in and will be put on the defensive. If not a simple jump-in, many characters have ways around/through the Kikoken at this point - Zangief EX Hand, Dhalsim slide, Blanka slide or EX Ball, Balrog EX Dash Punches, Bison EX Scissors…the list goes on. Knowing this, many Chun players will throw the Kikoken and then back up/back dash to give them room for another. I think this is a bad idea for two reasons - one it puts Chun closer and closer to the corner, and two it wastes her great poke and mid-range game.
Rather, Kikoken is a situational tool, which lets Chun either cancel out fireballs she doesn’t want to deal with, or force the opponent into doing something from full-screen. Case in point - Let’s take Chun U1 vs Ryu. With U1 stocked, if Chun is sitting on charge, Ryu can’t safely throw a fireball - even at full screen, he risks eating dash ultra. This gives Chun the ability to throw Kikoken, and force Ryu to deal with it. The safest/easiest option for him would be to walk backwards and let Kikoken evaporate in front of him - the downside of this though is that it pushes him to the corner. He can counter-fireball, but depending on when he throws it he may be at risk to eat a Hasan Shu/S.RH/S.FP. Neutral and forward jumps also pose their own risks. It’s a simple yet elegant way to either push Ryu into the corner, or force him to do something that Chun can potentially react to and punish.
This idea used to work well against Bison. With no fireball to cancel it out, Bison would be forced to either move backwards, block, or jump. Head Stomp/Devil’s Reverse became extremely risky for him if he wasn’t successful in psyching out his Chun opponent. EX Scissor would go through the Kikoken, but if Chun managed to block she would get free punish from this as well. This dynamic is greatly changed in Super, thanks to Bison’s U2, and most Chun’s picking U2 in this matchup as well. Chun can no longer throw Kikoken, and Bison gets to whiff Devil’s Reverse all he wants to.
Honda is another good example of this. At just under 3/4ths screen, he can jump over Kikoken and get a clean punish. Even if his jump-in is late and Chun is able to block, this puts her in the defensive, where now she has to worry about potentially eating chip damage to HH block string, Oicho, or getting baited and eating a combo. However at full screen the only good answer Honda has for Kikoken is to either move backwards, or neutral jump fierce. Both options slowly drive Honda into a corner, where Chun will be able to safely chase him down, or keep him at ranges she wants him to be.
On knockdown, it can be used to help apply pressure. A well-timed Kikoken serves to “lock” the opponent in place, preventing them from doing some kind of wakeup. While EX Moves and Ultras will go through the Kikoken, these usually come with added risk/meter burning, so many players will be reluctant to use it unless absolutely necessary.