What action is NOT recommended for improving the speed of an Apple device?

Running multiple heavy applications simultaneously is not recommended for improving the speed of an Apple device because it can significantly tax the system's resources. When several resource-intensive applications are open at the same time, they consume CPU and memory, leading to sluggish performance and potential overheating. This can result in slower overall performance, lag, and a less responsive user experience.

In contrast, regularly clearing cache, closing unused applications, and frequently updating software are practices that can enhance performance. Clearing cache removes temporary files that may slow down the device, closing unused applications frees up system resources, and updating software often contains optimizations and bug fixes that help the device run more efficiently. Therefore, running multiple heavy applications is counterproductive and detrimental to maintaining optimal speed on an Apple device.