Many CLI tools have a dry run option for expensive (time/resource wise) or risky commands (one way, irreversible or reversible only with a lot of effort). It would be interesting to see this become the default for some of them, with a separate flag `--now-i-mean-it` to actually execute.
I wish more tools had the option of dry run. Been using it with ansible quite bit in the past few weeks. Look ma I can mess up 50 computers all at once!