Why does Cachet need my home folder?
App Store apps can only see folders you choose; your home folder holds what Cachet checks.
Apps from the Mac App Store can only see folders you choose. Your home folder holds the caches, developer files and downloads Cachet looks at, so Cachet asks you to choose it once, in the standard macOS Open dialog.
Cachet reads names, sizes and dates only, never what's inside your files. Nothing leaves your Mac.
Cachet asked for my home folder again
This can happen after moving your home folder or restoring from a backup. Choose it once more and Cachet will remember it.
I chose the wrong folder
Cachet says so and asks again: it needs your home folder itself (the one with your name), not a folder inside it.