When it comes to making things "faster", an easy thing to reach for is concurrency. GCD and NSOperations make dealing with threads a breeze and if your task lends itself to concurrency then it makes a lot of sense.
The thing to remember is, once you've introduced concurrency into a system, it's your responsibility to make sure your data stays in sync. Depending on the application, not doing so could result in hard to debug problems ranging from inconsistent UI to catastrophic data loss.
Since we want to avoid all of those things, it's best to go into multi-threading with synchronization in mind from the start.