In order to perform Takemusu Aiki, there are three aspects that must be attained: There is the spiritual aspect - skill in deconstructing the Ego-Tripartite; there is the strategic aspect - skill in establishing fields of advantage; and there is the tactical aspect - skill in sound technique. The more present and the more mature or accomplished these aspects are in a deshi, the more Takemusu Aiki can be manifested within ever increasing extreme conditions. The less present these aspects are in a deshi, the less Takemusu Aikido can be manifested under such conditions, the more the cultivation of these aspects will require and benefit from inserting control devices into Jiyu Waza.
The introduction of control devices allow for Jiyu Waza to take on a progressive learning format. Probably the dumbest thing a teacher could do is teach a deshi form after form and then expect them to function inside of a fully live training environment. After all, the point of Jiya Waza remains the same point as for Kihon Waza: To train the deshi. The goal of Jiyu Waza training is not to simply survive such training or to achieve victory over one's training partner. Jiyu Waza, like sparring, is not contest.
The introduction of control devices into Jiyu Waza is not a subversion of Jiyu Waza training, but a progression in such training: This is how things should be looked upon.
Control devices will lesson the requirement for the aforementioned aspects to be fully mature within the practitioner. They in turn allows a deshi to move beyond survival reactions which are antithetical for good form, and to thereby actually learn something and thus improve. However, a caveat:
The more control devices included in Jiyu Waza, the easier it is for a deshi to usurp the training - such that one is not learning anything capable of performing at a full Jiyu Waza level. It is for this reason that a teacher already capable of performing Takemusu Aiki in full Jiyu Waza training environments is so vital to a deshi’s progress. Only such a teacher can see where any or all of the three aspects remain flawed and/or incapable of making the jump from controlled live training environments to fully live training environments. Without such a teacher, “Jiyu Waza” becomes a farce of what it is meant to be.
In this way, Jiyu Waza is totally different from Kihon Waza. Anyone can teach Kihon, for repetitive practice, commitment, and Shoshin can always make its way through bad teaching and bad instruction. One can learn form even from a video. But, the application of form, which is the reconciliation of form, can only be learned through another that already has such skill at reconciliation. Anyone can read and copy the sutras: Not everyone attains Samadhi.
Please watch the video for further details:
https://youtu.be/RaW2mvyk1Nw