I can’t speak for everyone, but my veneers are as thin as possible as they are there just for looks. I typically grind them down below .025 and have gone as far as .018 on some species. Almost insignificant other than they add their size as part of the stack.
That allows me to make the core lambs as thick as possible, whether they be bamboo, hard maple, padauk, zebrawood, etc. With the cores, I am looking for springy, and stiff, straight grain samples that are going to be as consistent as possible.
Hope this helps