When you're IO or network / database bound, then, you won't notice.
When you're just CPU bound without having to cope with lots of memory transfer / throughput, then you won't notice.
Without a doubt, there are many apps that don't need this pure speed, but for specialist apps and even general apps on the desktop (compare firefox to chrome and safari for example), you can notice the difference quite distinctly.
In my experience writing high performance applications for the VFX industry, where both memory performance AND memory compactness (so you can fit as much in memory as possible) are important, when profiling applications, I've found that maybe 70% of the time it's the memory allocation / deallocation that's the actual bottleneck, not actual calculations.
Being able to separate stuff into separate allocators based on different use cases adds complexity, but gives huge benefits when you're memory throughput constrained.
When you're just CPU bound without having to cope with lots of memory transfer / throughput, then you won't notice.
Without a doubt, there are many apps that don't need this pure speed, but for specialist apps and even general apps on the desktop (compare firefox to chrome and safari for example), you can notice the difference quite distinctly.
In my experience writing high performance applications for the VFX industry, where both memory performance AND memory compactness (so you can fit as much in memory as possible) are important, when profiling applications, I've found that maybe 70% of the time it's the memory allocation / deallocation that's the actual bottleneck, not actual calculations. Being able to separate stuff into separate allocators based on different use cases adds complexity, but gives huge benefits when you're memory throughput constrained.