I built a memory allocator for testing not too long ago that only allocated but no-op'd deallocate(using the C++ Allocator interface). It was quite amazing that it resulted in a 25-50% performance boost in many cases I was testing. It's not for real code as you only get destruction but not deallocation. It let me pull that part out of the tests to get a better view of the performance
this is why composable allocators are fantastic. You can request a dynamic memory slate for a given context, then allocate as you wish, no-op delete, when you're done with the context, you delete all of them in one go.