John Gerlach wrote:
It surprises that folks shoot macro handheld. I have shot at least 1/2 million close-ups shot and never shot one handheld."
Try it sometime, you might like it.
"Especially now that I stack so much, and use flash for various reasons, I don't see how I could work handheld into it".
For focus stacking a tripod might be required, but a flash generally takes away the need.