Disclaimer
I guess everyone who saw the movie noticed the elaborate trap, and maybe even thought about it. This is how I see it.
When the trap was triggered Irene Adler was in dire straights. The stake was to get the machine stopped before she died. We get graphic visuals showing us what is at stake, as pig carcasses gets sawn apart. Now did you notice where Sherlock was looking?
He saw the mechanism to the trap, and he saw what was holding Irene fastened. At this point he had two ways to approach the problem, by freeing her or by disabling the mechanism. Note how the clock is ticking, and we have a time limit for the trap. This makes it more tense than just a pressure plate and a save for half damage.
The most delightful part of how this trap was set up was that violence was always an option, as well as a more refined or crafty one. The mechanism was visible and you could poke at it and try to stop it, you could grasp how it worked and try to shut it off. A very real option was also to just jam something durable into the gears and make it stop or at least slow down. This gave it a possibility for multiple types of gamers to solve the issue. Yes, we also had the chains and the lock. The lock was visible, but you had to reach above Irene's head to get at it, and it was moving. Clearly an oportunity for inventiveness, and also sweeten the payoff for successfull disabling by putting the character who tries to solve the puzzle in the line of danger. Everyone loves to succeed when there was a threat of real danger. Naturally, you could hang onto Irene and just try to apply force to those chains and break the hostage loose.
Did you see all that?
I think the way this scene was set up was a marvellous set piece trap that any DM worth his salt should study and emulate. There are multiple venues of approach, and you can work one them more than one at a time. Violence is an option and there is a time limit. Very important for all this to work is that there are nothing hidden. We all see the mechanism clearly and the only thing left is to to try handle the situation. I'd would love that in a game!