Hi there.
When we started our site, we had no idea about child themes - and never had any customization that would require one.
Now we have to modify some templates. And as far as I understand, Best Practice is to do that via a Child theme.
Before I embark on that little adventure: What will happen to our site when we switch to the child theme? Do we have to redo our custom CSS for example?
(The next site will have a child theme from the start, just to make sure.)
I’ll be on vacation the next two weeks, so no need to hurry with the answer 
Happy holidays and a good start into 2018,
Jens