There has been a lot of misconception regarding this technique. Redditors, for example, have been arguing if ice in your bong gets you higher than a regular one or not. In reality, it doesn’t.
When you heat the cannabis bowl and make a toke, smoke passes through the ice notches/catchers. Ice works like a buffer that absorbs excess heat from the weed vapor. It traps its thermal energy, not letting it enter your mouth, throat, and lungs.
As a result, the weed smoke gets chilly. It loses its harshness, and the flavor receives a unique ‘frosty’ tone that makes the soft blandness a bit more enjoyable.
However, you can’t find much scientific research on the topic. And opinions vary — some say it’s totally safe, others that it can trigger bronchitis. I guess you just need to bong responsibly and not too often to stay safe.