In reply to Lorna.

I suppose it will depend on your approach. There are tons of things that can be done directly via the site editor. However, for those things that cannot be done, yes, I would recommend a child theme.

That's been my recommendation in the past too. I've always used the custom CSS option for quick fixes when I didn't have my entire dev environment spun up. Then, I'd later add those directly to the theme or child theme's stylesheet.

But, you can always go to the wp-admin/customize.php URL and make changes like that for a client.