These days, most so-called “anonymous apps” (yik yak, rumr, etc.) are not ultimely anonymous. They’re anonymous, although only in the sense of individuals.
Most of these services/network are only about talking to people near your location. You might as well use Facebook. You “might” know the person who you’re talking too, and, although it’s only a possibility, that defeats the purpose of anonymity. If location weren’t applied, the chance would be negligible, but they had to use location.
What’s scary about this is the possibility for gossip, rumors, etc. Especially since you know the community. Might as well call them “anonymous bullying apps.”
They’ve had bad effects on many people who are targeted. Especially major lost of repution without repercussions for the perpetrators, since, well, they’re anonymous.
Of course, I’m not trying to say all apps are like this. That’s not what I’m talking about. There are some genuinely anonymous apps, but those ain’t popular. “Anonymous bullying” apps are way more popular because people can talk shit about people who they hate and are jealous of, without any karma coming to them whatsoever.
So remember, ones with location based services, with “people you know” are essentially anonymous bully clubs. They’re very despicable.