1) interesting solution to the double spend problem, and therefore usable as a currency (just like gold coins, apple macbooks, rolexes, ... are usable as a currency)

2) The government "controls" spending on drugs by checking the payments made to suspicious parties, not by checking the contents of packages coming in. In other words, bitcoin is a "legal hack" that basically allows you to get heroin delivered to your door like an Amazon package. Or guns. Or poison. Or illegal medicine/performance enhancing drugs/...

3) untraceable or less traceable payments. Which are basically allowing for criminal acts to occur on more scalable levels like hostage taking, for computers and of course for real. [1]

1 is probably played out at this point, but 2 is very much alive. (e.g. [2])

[1] http://www.telegraph.co.uk/news/2017/05/12/nhs-hit-major-cyb...

[2] https://cointelegraph.com/news/bulgaria-seizes-enough-bitcoi...