Yellow Swordfish said
…yes – you should expect errors if you try and just run the reboot.php file in the browser.
Phew! 
If the combined/compressed cache is working for you then this is actually even better than anything else.
Great. Out of curiosity though, wouldn’t the CSS Only custom theme also serve up the compressed/cached stylesheet, or is that a function of the PHP version?
Thank you again for all the clarification about whether my notion of a CSS Only theme being lighter/faster is actually on point.
I do want to avoid all the themewerk involved, and I certainly like how my child theme will require minimal if any edits over time. Just trying to minimize any “extra” PHP wherever I can. (SP is not the only plugin/theme I’m tweaking for optimization.)
If you do not already use it then using the Script cache is also to be recommended as long as it causes no issues.
Yup, got that enabled. Thanks for suggesting I check.