As a developer who does a lot of work with WordPress, I run into the following scenario all of the time:
A developer has made custom changes to a theme, and following an update to said theme, the custom changes go “poof” and are gone with the wind!
Then comes the interesting part: determining if there is a backup of the files containing the custom code, determining which files contained custom code, obtaining those files from the backup if it exists, and then reincorporating that custom code into the newly updated theme or plugin. However, if I’m the one doing the reincorporation, a child theme will be getting created, from the word go.
The reason is that creating a child theme will prevent this same issue from arising the next time an update is released for said theme.
While this approach isn’t fool proof, and can cause some issues with the new version of the theme, they’re easily remedied! The best part is, you do not lose code. Worst case scenario, the developer will have to copy and paste the contents of the new version of the files in question into those same files in the child theme, and then situate the custom code appropriately. This is much easier to deal with than having to find lost code, or recreate lost code if there is no backup available, all the while, leaving your site gimped and missing the custom code, that probably does something fairly important (or you wouldn’t have had it custom coded to begin with).
The next time you need a developer to customize any theme files, make sure they are using a child theme, and if they don’t plan on using a child theme, request that they do, ask them why they do not use child themes, and promptly replace them with someone else more savvy with WordPress (if you really get brave, I’m available for such rescue operations).
Digi Purpose 