the buffer managemnt is just different pattern and style of code thats more low level. when you care about performance and cpu cache, you have to make sure that actual physical memory gets computed at same time as other memory near it so there is less latency.
the primary motivation isn't latency but complexity. People do in some applications free or allocate collectively because they have interrupt times in mind, but most of the time when you manually manage memory the issue is mental overhead, so people gravitate towards models they can keep in their head.
Allocating in large chunks is often not very performant which is why people came up with tools like the borrow checker, you often want to allocate and deallocate dynamically on a need-basis but that's exactly where bugs occur.