Problem Statement
Which of the following describes the `DispatchQueue.main` vs `DispatchQueue.global()` in Swift concurrency?
Explanation
In Swift and iOS development you use `DispatchQueue.main` to execute work on the main thread, especially UI updates. `DispatchQueue.global()` (or other background queues) is used to run tasks off the main thread to maintain responsiveness. Proper use of concurrency avoids UI freezes and ensures performance.