Sometimes I want my tweets to be directed at a subset of my followers; a useful/interesting Python link for colleagues, an Echo Bazaar comment for other players, that kind of thing.
The way @replies are handled has created the possibility of filtered communication. I can direct messages at a particular user knowing that only those who follow it will see the message – by creating specific ‘group’ accounts and directing messages at that user I can semi-privately communicate with that user’s followers. I can’t say anything that I don’t want the curious to see (my tweets are still there on the public timeline), but if I want to shield my broader range of followers from something I know they won’t be interested in this is a useful approach.
An example is the @isotoma user. This user is pretty much exclusively followed by Isotoma staff – if I direct a message to that user only Isotoma staff will see it, allowing me to tweet Python links to my heart’s content, knowing the intended recipients will get them without putting off those who wonder what the hell I’m talking about.