Here’s what I found out, with appreciation for the comments to the question.
I write WP code (themes and plugins) and non-WP PHP code (for non-WP sites). In non-WP sites, I include those statements in my ‘include’ file to ensure POST/GET sanitation, even though I try to sanitize the fields elsewhere. So, sort of a ‘sanitize backup plan’.
But putting the code in a WP plugin file too soon kills the plugin’s settings screen and/or the front end; more often on the front end with the plugin enabled (result is sometimes a white screen).
So, for WP plugins/themes, I will ensure sanitization of individual POST/GET fields, rather than the above code.
In non-WP sites, though, the above code is benign – sort of a double-check-sanitation thing, even though I try to remember to sanitize POST/GET fields before using that data.