Here’s an example. I have a program that does a lot of memory allocation and reallocation. The memory management strategies in modern OS’s work wonders on this, better than a custom allocator I can write in a reasonable amount of time. In bare metal os I would lose this all for the advantage of not loading an os that tends to stay out of the way unless needed anyway.
Where I see use for this is more likely in situations where time to boot is critical but actual resource requirements minimal. Things like a simple kiosk system or embedded hardware.
It's likely that if memory allocation overhead is part of your bottleneck, that using malloc() is actually a bad idea. Other management strategies such as arenas or rolling buffer will likely perform better. They're also trivial to implement ad-hoc.
Of course, you might arrive at the conclusion that the complexity overhead of custom allocation strategies[1] might not be worth it, but in this case, it means speed is not really an issue.
[1]: as well as, maybe, the necessary redesign of the application to fit those allocation strategies more elegantly.
But I wouldn't be so sure to claim that such a pool, implemented in assembler on an OS that leaves everything to you, wouldn't outperform the os allocator you refer to. After all, there is fundamentally less information to manage.