Where I train it's always the junior grade who goes first, except in paired weapons practice we reverse with the higher grade swinging the lump of wood at the lower grade first.
There are reasons one could argue the benefits of practicing either way but for me; senior student should be able to provide the appropriate attack as uke to allow the lower grade to "feel" what is expected as well as get straight into putting in to practice what they've seen.
With weapons, demonstration of the movement in a controlled manner can help to keep the dangers of bokken colliding with wood (in the case of my head) by emphasising the exercise over the exuberance.
I'm not saying it's the only way or the right way, just the way that I do things
I think this makes quite a bit of sense. It's very important, especially for the newer students, to understand the proper fit of technique and attack.
The idea that we need to force our techniques on someone is bad martial arts, in my opinion. Flowing around the attackers force, to find his weakness, is safer, more feasible, and a much more demanding practice. Training to feel the appropriate response physically, helps to train us to mentally/emotionally put this kind of practice into our everyday lives.
In short, it's a more sound practice, both martially, and practically (in daily life).