HEIC and WebP: two efficient formats that don't talk to each other
HEIC is efficient on the iPhone, but almost no website accepts it as an image — browsers don't render it the way they render a JPG or a WebP. WebP, on the other hand, is the format Google recommends for the web: it compresses well and every modern browser supports it.
Converting straight from HEIC to WebP skips a step: instead of going to JPG first (heavier) and then to WebP, SMALLIMG decodes the HEIC and encodes it to WebP in a single pass, right in your browser.