… (enumerating the objects on several threads in parallel). This isn't always useful, depending on exactly what you are doing in your loop, but for cases where you are doing a lot of work per item, and where you don't care about the enumeration order, this can yield a significant performance boost on multicore processors (which all modern Macs and iOS devices have). ….. iOS Developer Tips Newsletter. Email: Subscribe. Selection of the week's most popular posts.