In Aikido we learn from our partner, if your partner is not letting u perform your tech, then its bad for both of you and its bad ukemi, if u are both training on switching from one tech to the other, then uke should provide only moderate resistance so nage can feel and redirect to another tech, aikido is cooperative training so all can learn.
Agreed. Aiki-do practice is Yin practice. Both partners practising pre-agreed movements and even at randori at higher level. I have been training for 17 years and it is not in my nature to jam anyone's technique unless (as Ruth has indicated) I feel the tori is about to inflict injury to me by not availing to me the space to take ukemi or by excessive use of force. As a tori, I sometime initiate a bit of resistance ("to pull in the slack") in order to search for my partner's center. As a uke, I am very conscious of my action and I know when to offer constructive resistance but never destructive resistance.