Some fields reference attributes directly. When the referenced attribute
has the requested type and domain, the captured/stored attribute can
share its array, avoiding the cost of duplication and reducing memory
usage, at least temporarily until either attribute is modified.
This only works when the attribute doesn't need validation and when
the selection input isn't used, since those potentially need to change
values in the arrays.
I saw this save 200MB and 11 ms of copying for a simple grid with
16 million points (creating the grid takes about 60ms).
Pull Request: https://projects.blender.org/blender/blender/pulls/107357
b54398c16c