I wrote a post to explain the reason, I then realize that since the roundhouse kick is not emphasized in the WC system, my post may not apply to a WC thread.
Here is my reason why I want my opponent to switch sides in fighting.
When my opponent and I both have right side forward (uniform stance), my left back leg can only kick on his back (not a good target). My right leg is too close to my opponent and roundhouse kick is not powerful for that distance. I can use front, or side kick, but since my opponent stands side way, my target is limited.
In this pic, the person on the right kicks on his opponent's back which is not a good target.
When my opponent switch sides and changes from right leg forward into left leg forward, his center line will scan across my body. If I can catch that good timing, my left leg roundhouse kick can hit on his chest (a full target).
In this picture, the person on the left switches side from right leg forward into left leg forward. The person on the right kicks out his left back roundhouse kick without any hesitation.
In sparring, you either wait for this opportunity to happen, or you try to create this opportunity for yourself.