An application that uses 64-bit pointers but doesn't need 64-bits of virtual address space is wasting physical memory because your pointers are twice as large. The application would waste physical memory pages and memory bus traffic just to store 64-bit pointers with lots of unused zero bits like 0x00000000ffffffff.

> If an application is not memory intensive, why would you care if there is 'waste'?

Performance. What other reason do you need? (Using cache more efficiently makes programs run faster).

Because there is a finite amount of cache at each level.

'not memory intensive' is an ambiguous term. he meant 'does not use a lot of memory, but may access what memory it does use quite a bit'. you meant 'does not access memory often, and performance thus does not depend much on memory access latency'.

Ten not memory intensive applications, combined, can easily be memory intensive.