As theducks says it is really about what floats your boat and how obsessed you want to be about the books in your library.
As the author of the plugin I only use a tiny fraction of the checks, mostly metadata related to spot where I have added books that aren't consistent with my naming standards.
Almost all the checks were written 12+ years ago back was also when Sigil was very limited in what sort of validations it could apply, so people were interested in running rules about the internal structure of their books in bulk for various reasons. Ereaders have obviously matured over time - bugs and quirks that particular issues tripped things up on are no longer likely to be the problem they once were.
So long as the books are readable on my device and scanning through the library on what to read next I am not seeing "eye sores" that is all I care about
