Different CS props have different operating characteristics, and the pilot should have some awareness. In short, if the prop/engine are still turning (powered or windmilling), the pilot should expect to have control of RPM, and may (and should) select full coarse/low RPM if a power off forced landing is committed.
The only reason to not select coarse pitch, would be if the pilot wants the drag of the fine pitch windmilling prop to assist in a steep descent into the "spot". In that case, the pilot should have practiced how the plane glides and flares that way.
I have recently changed propellers, and the new one is much more draggy than the one I replaced. I have experimented with glides in coarse, and doing that makes a great difference in how the plane handles in a glide. In coarse, I "get back" about 600 FPM descent rate compared to fine pitch. While experimenting, I did move the mixture to ICO, and mags off, no change in propeller operation. I was still flying a "turning" engine though - seized would be a different story.
Note that some feathering propellers cannot be feathered at RPM slower than around 1000. This means that if you're going to feather it, get it done before the engine coasts to a stop. Some feathering propeller systems have unfeathering accumulators to provide the oil pressure required to move the blades toward fine pitch for an inflight restart. Starting a feathered engine in flight is messy.
whilst on a flight are you able/allowed to practice, for example, a forced landing? If you are, how do you do this safely? Do you have to tell ATC what you're doing?
As often as air traffic seems to permit, ask ATC if you can fly a circuit which will include a practice forced approach. Otherwise, fly to a quite, uncontrolled airport where you have some circuit and runway to yourself. Then keep a close listen for other traffic arriving while you are focused on your practice!