During High-quality Mode, the laser moves across the whole length of the job at a constant speed, marking only the defined areas for engraving. Jobs get engraved at the same speed through the entire engraving surface. The final result is an even, clean laser engraving.
When High-quality Mode is not active, the laser head typically moves at a faster speed but only over the width of the actual area to be engraved. The final result has different exposure times and deeper engravings in some sections.
Summary: When you want a high-quality engraving and the engraving time is not crucial, always activate High-quality Mode.