Just a hypothetical tale that did not happened (really...):
There was a guy in one country in some post-communist Eastern Europe country who was still using DC++ (yeah, lol, in 2012...) and he shared a lot of copyrighted music and video files and therefore one day police came into his flat and seized his computer (it had some chilling effect on local community...). He was not only using DC++, but also bittorrent. The forensic specialist searched for all filelists in all filesharing applications to make a list of files and to calculate "damage" he caused. As his DC++ and torrent client settings were not encrypted, they got everything he had downloaded (and thus also shared) and added it to the "damages" list. Yes, they came after him because of DC++, but they added BitTorrent shares too when they caught him. They also added all pirated software he had to the damages, because once it was prooved that he illegaly shared at least one file, then it means that house search warrant was justified and evidence obtained this way was legal. Not only did he have to pay big damages to local MAFIAA, he also got two years probation. If he had encrypted all file sharing programs directories (eg. in TrueCrypt), then forensic specialist would not have obtained file list. Even if the files were on the computer, in that particular country posession of video and music is not illegal, only sharing. Because there would not be an evidence of wrongdoing, he could lie to the court that there was a family member (he can legally refuse to say who was that) on the visit who downloaded the data and then shared it with him on local network. Then it would mean that he himself was innocent and thus the search warrant was not appropriate and any further obtained evidence could be dissmissed as a fruit of the poissonous tree and the fact that his computer contained pirated software (possession is illegal) could not be used against him. Maybe they would seized the computer (as it was a tool of criminial act - possesion of pirated software, person cannot be sentenced but evidence remains seized), but they could not at least sentence him.
While I do not promote illegal activity, any person (dissident etc.) might benefit from such security feature too. Would you prefer if your kids in their notebook had their torrent settings encrypted or not when police knocks on your door? Many persons would have not been sentenced if their filesharig clients settings were encrypted. I studied say about 15 court cases and always the most important evidence is filelist obtained from the settings. For example if there is a folder with video AND that folder is being shared in DC++, then the defendant is guilty of announcing all copyrighted data from that folder to the public, but if there is only the folder with copyrighted data but not the settings, then nothing happens to him. If the client also track share ratio, then it can be used to exact calculation of damage. Damage = price in shop x upload ratio for that particular torrent. Having .torrent file itself is not much a problem, it only indirect evidence that defendant might have been torrenting, but then he can say to the court that he did not uploaded anything, only downloaded as there were many peers. Of course it's better to delete and wipe .torrent files too...
The proposal aims at making forensic analysis (obtaining evidence) harder, not to prevent being caught. By announcing it in the client name it should be obvious to parties who are fishing IP addresses that if they send police there, they will not get anything. You could also use such feature to hide your downloads from girlfriend/boyfriend/boss/teacher/parents/any authority so it does not aim only at making criminal investigation more difficult, but any investigation by any person. For example if you misuse your work computer to download music and video to external storage while night then there might somewhere reside information on what you downloaded. Better if it is not here so that remote admin cannot easily see it (and we have another case justifying such a feature, while immoral it is not illegal...).