Sending cold paid traffic straight to a product page is the most common money leak in e-commerce. The product page is designed for someone who already knows what your brand is. The person clicking an ad does not. They arrive mid-thought, from a video they watched for two seconds, and the page opens with a price.
A landing page fixes the order of operations. It picks up the thought the ad started, makes one argument, handles the two objections that actually stop the purchase, and then asks. It is not a prettier product page — it is a different document with a different job.
The page has to continue the ad, not restart it
If the ad was about the heat, the page opens on the heat. If the ad was a person unboxing, the first thing on the page is that moment, not your logo and a navigation bar. The single biggest lift usually comes from removing the gap between what someone just watched and what they now see.
This is also why one page per angle beats one page for everything. If you are running three creative angles, the honest answer is often three thin variants of the same page rather than one page that tries to serve all three and commits to none.
Built to be tested, not admired
A landing page is a hypothesis. It should be structured so that the headline, the hero, the offer block and the proof section can each be swapped without rebuilding the page — because within a fortnight you will want to swap at least one of them.
Conversion events are wired before launch, not after the first disappointing week. If you cannot see which section people stop at, you are testing in the dark and the page might as well be a coin.
Mobile is the page; desktop is the accommodation
Effectively all of this traffic is on a phone, held in one hand, in a scrolling posture, with the sound sometimes on. That is the design target. The desktop version exists because a few people will open it there and it should not look broken.
Practically this means the hero is designed at 390px first, text is sized to be read at arm's length rather than to look balanced in a mockup, and nothing important sits in the bottom quarter where a thumb and a browser chrome live.