That's actually a grey/black hat way of boosting your ad sales numbers, even if you didn't click.
You buy x at y store, y store has an ad buy with ShadyAdCo. If you see product x in an ad within z time afterwards, it counts as an influence towards your purchase. ShadyAdCo just made money, and y store can give record numbers.
You buy x at y store, y store has an ad buy with ShadyAdCo. If you see product x in an ad within z time afterwards, it counts as an influence towards your purchase. ShadyAdCo just made money, and y store can give record numbers.
EDIT: typo