Hi Joe,
1. The reset settings button resets all settings you see on that page, including the custom homepage and Post Type Archive metadata on the page. The reset button doesn’t affect the site’s stored post/term/user metadata.
Here’s a little trick if you can distinguish green and red: Checkboxes with a red border are “do not use unless you know what you’re doing,” and checkboxes with a green border are “this is ticked by default.” This appears more clearly on Firefox.
But if you have difficulties discerning colors, here’s a long screenshot with the defaults shown. Your settings may differ slightly depending on the plugins and theme you have active.
2. You’ll overwrite the generated description by entering a custom description. I do not see a problem with this. The generator is optimized for performance (sub-millisecond generation) and accuracy (it understands HTML), but it can’t come close to human intelligence because it isn’t attached to a neural network.