So it is like allocating an array of objects but I guess it does not have to be homogeneous, i.e. you can decide after the initial allocation what objects you want to live in your chunk of memory. Allocation gets simpler as you just have to move one pointer forward past the newly allocated object. Memory usage would actually remain the same or even increase - ignoring the overhead of data structures to track allocations - as the lifetime of objects is now tied to the lifetime of the arena. You could get essentially the same behavior from a normal per-thread allocator if you never freed anything and the allocator would satisfy all allocations from a single pool. You would of course still pay the management overhead and have to free every object individually. More interesting scenarios arise when you use several arenas with different lifetimes or mix arenas allocation with normal allocation.