No, it's total nonsense of course. If you imagine a web browser with lots of tabs open, if someone closes lots of tabs they might be doing it specifically to f

No, it's total nonsense of course. If you imagine a web browser with lots of tabs open, if someone closes lots of tabs they might be doing it specifically to free up memory. Even going over physical memory is not a death sentence anymore because of fast SSDs being used for virtual memory. Because that is slower however, freeing up memory will still speed everything up, even if the maximum memory used needs to go over physical memory. The OS also caches memory mapped pages of files, so memory used means more disk IO from that standpoint as well. Even disregarding all of that, heaps get fragmented, and if many virtual memory allocations can be given back to the OS, the next time more memory is needed it will be allocated in large, 'virtually contiguous' chunks that start out without fragmentation.