Steganography, similar to many modern day technologies can be used nefariously; however there are legitimate uses. For example, reporters looking to privately publish their works. This is especially important where the location of the reporter means that communications maybe blocked or monitored. They require the facility to disguise their communications in order to get the news to the masses.

Terrorism
Reports previously have been in the news detailing how terrorists have communicated using videos as a cover file.Computer forensic experts from the German Federal Criminal Police (BKA) discovered a pornographic video file name “kick-ass.mov”, when they arrested a suspected Al-Qaeda member in Berlin, 2011. They had found over 100 files detailing operations and plans within this video; such as “Lessons Learned”, “Report on Operations” and “Future works”. Fortunately for them it was not encrypted. This could have been uploaded to one of the 4.2 + million possible pornographic sites on the internet . Thus making the carrier files extremely accessible to those who know where to look, and a needle in the haystack operation for others.
Data Exfiltration