I tested the students from the middle & highschool class on Tuesday out in the field at the back of CFHS. It was a cold afternoon and we were racing for time against sundown, but everyone got their chance. Only one student, Reed, actually cut for a test and did well. The three others had their first chance at cutting after about 2 years each of studying.
It's especially relevant for younger students--these guys started at age 12 or 13--to practice swinging only a bokken for a while before ever touching a real sword. Typically they don't have the physical strength for it, but more importantly they don't have the technique practiced well enough yet.
I think holding off for months if not years of just bokken practice before target cutting, is just as relevant for adult student. They usually have the strength, but until they practice for a while they don't have control of the technique. So combining strength without technique is just inherently dangerous.
In any case, there are usually other surprises for the first time cutters:
1. It can hurt the palm or wrist - yes it can if you hit it in the wrong part of your swing, have the wrong grip or weak wrists, or even don't swing fast enough (thus not overcoming enough inertia). You can also hurt the palm if you're not used to swinging a sword that has wrappings (cloth or leather) on the handle / tsuka. The guard / tsuba can also give you blisters from rubbing against your fingers or wrist. I've seen first-time students get blisters from just swinging a sword.
2. Swinging a katana throws them off balance or they overswing - the weight of the sword is usually much more than the bokken and it's weight-forward meaning the weight is typically nearer the tip. I think swords should be this way because it lets more power go into the cut (versus swords that are counterweighted or balanced towards the handle)
3. You can cut into a target but not cut through - there are several possibilities here: a) too weak a cut; (b) the wrists were out of alignment or not strongly held and bend; (c) they shakkuri or turn the edge while in the middle of the cut
4. A steel sword can bounce off a small target made of grass - People don't always believe me when I tell them this until they do it or see it themselves. Usually, it's a kesa where the ha-suji (angle of the edge vs target) is too flat and they swat the target with the flat more than cut into it.
5. Goza smells - :) Yes, it does and if you don't clean your sword afterwards, so will your sword
6. Wet goza can stain my sword - If you don't clean your sword after cutting soaked goza soon after cutting (within hours), it can etch onto your sword, and require a good polish to remove. It's ugly but unless you do it frequently it won't damage your cutting edge (but damage the value/niceness of your sword)
7. I keep finding goza bits everywhere - the straw is insidious. If you cut indoors it will remain in the cracks and corners of the room no matter how much you try to clean. Live with it or count on cleaning up multiple times. If you practice outside, it's a good behavior to clean up.
There's probably more, but I forget right now.