I really do not believe chi sau "sparring" is actually sparring but meant to refine skills, build sensitivity and such. If you aren't testing your skills in at least a controlled situation, full speed, using the principles of wing chun to "win" or overcome your opponent then it isn't really sparring imo. Sparring is used to refine your skills in a more "fight like" situation. Of course sparring is controlled and not an all out fight but it's merely a tool to ingrain your skills. Pretty much the same as chi sau and in this sense you are correct but it's not a "fight like" situation and preparing you for everything that goes along with that. Just also a tool to enhance, ingrain, refine and build sensitivity.
As I have said many times chi sau encompasses rather a large territory , it can be anything from light compliant rolling to the more aggressive non compliant full speed trapping and striking.
Tsui Seung Tin has stated that it is Wing Chun's own unique method of sparring to prepare for close range combat.
You go into his school in Hong Kong and you will be doing hours of it.
When two well trained Wing Chun guys engage from distance , what do you think happens?
I will tell you exactly what happens , one or both of them initiate kicks and then it ends up straight into chi sau range , they will start punching , one will put up a Seung Bong to defend and then it's into Lap Sau until one can trap the other and strike through.
If your good you can be defending upstairs with the Lap Sau and low heel kicking his knees/shins at the same time.
If you want to do that type of sparring from out of range then it is probably better to have one partner using non Wing Chun attacks , rather than both Wing Chun guys using Wing Chun because as I said it always ends up into chi sau sparring anyway.
Chi Sau is a very good defence mechanism , we project a revolving cone like structure with the point focused at the opponents centerline .
If we do this properly with the correct arm structures and an even flow of force , the opponent cannot find a gap to strike through , a bit like a shield.
Yes it is used to develop attributes like sensitivity etc , but the structures are also directly applicable to real fighting.
We are working out the best way to use the strong points of our arms to attack the weak points of theirs.
I totally reject this passive version of chi sau for anyone other than beginners , once you can do the basic movements and have a half decent stance you should be moving around , pivoting , and executing different traps and attacks while rolling.
How are you ever going to find out where the gaps are in your chi sau , whether your Fook Sau is on center or if your Bong Sau is crossing over a bit if no one ever tries to trap or strike through these structures and shows you these errors.
Take for example a very common attack done in chi sau , the palm strike to the chest from the Tan Sau position , it is one of the movements used in single arm sticking hands .
A very simple attack and quite easy to stop in single sticking hands when you have to only worry about one hand , but when you start doing double sticking hands and have to concentrate on both your hands doing different things at once and also adding moving around and randomness then it becomes a whole new ball game.
What was an easy attack to stop in single arm chi sau suddenly has become a lot harder to stop in double arm chi sau.
In time as your skill develops you will also be able to stop this attack even while your other arm is defending an attack at the same time.
But unless your partner is at least some of the time trying to strike your chest with a full speed and full power palm strike to your chest while you are moving around and rolling , then you will probably never develop the precision an focus needed under dynamic conditions to be able to counter that palm strike because all your training has been conducted in static , controlled , compliant chi sau.
To be able to stay focused and keep that Fook Sau dead on center even when the action is speeding up and you are moving around is another level of skill altogether
If all your training is just standing there rolling in isolation and no one moves around or attacks , how on earth are you ever going to learn to deal with force , how are you going to learn how to move your body mass and affect your opponents structure.