Giving in T'ai Chi is important. I'm talking about giving energy.
Giving energy is giving whole heartedly. Without this there is no development, no sincerity, no creation.
I once asked a student to push me on my arms held in press posture. He pushed me just with his arms at first, so I could only move him slightly. The next push was with more force but still came from the arms. He was holding back within himself. I was looking for the full committment from him, mind, body, energy. When he did, I was able to uproot him cleanly. Because he gave from himself without holding back.
The interaction and exchange of energy is part of the learning process. It is a transmission. By holding back, nothing can be gained or learned. Except , perhaps, how to be dull. It is the same for all martial arts.