[ Sherlock really shouldn't down too much considering his father had died due to a heart condition, but that connection either doesn't come to Sherlock or is stubbornly ignored. (He's more his mother's son that his father's from what he knows of his father. That's Mycroft.) ]

As you said, it is commonly used to kill someone and avoid detection. I've seen used to good and for evil. You have to gather all the facts to truly understand a situation because it could be a tool to remove a rival from the picture or escape an abusive relationship.

There is also cyanide which kills far quicker. That is much more obvious and more likely to be noticed.