The memory usage is based on objects initially placed in the layout. If you delete them and create them at runtime, then the runtime memory usage hasn't actually changed, but C2 will estimate the memory usage being less based on the initially placed objects. Basically the memory estimate assumes you don't create any objects at runtime.
It's also a bad idea to delete objects you actually use from the layout, because if they are initially placed, C2 will pre-load them when the layout starts. If they're not initially placed in the layout, it will be forced to load them at the moment you create them, which can jank the game.
tl;dr it will make things slightly worse.