I know, ChromatiCraft runs somewhat smoothly.Most of CC's filesize is textures and sound files, not all of which are even used. I am not going to remotely claim it fits the description of a "so light it has no performance impact" mod, nor that it has "no features with which someone could do anything unpleasant", but raw filesize is not an indicator of computer load.
File size might affect loadup time though, then again CromatiCraft has only added 10 seconds to my load time. And high texture resolutions might impact rendering a bit on poorly built or weak computers.
File size isn't a be all end all deal but it would have some sort of impact.