Why is running ethernet and power in the same conduit bad? Other than for possibly signal interference for the data? I would love a general book recommendation

Why is running ethernet and power in the same conduit bad? Other than for possibly signal interference for the data? I would love a general book recommendation, if it exists, for "common construction codes ELI5". It would be better for helpful best practices to be accessible and easily comprehensible rather than be bound up in some municipal website.