One Generic Ad to Every Website Visitor
The person who added three items to their cart and reached checkout is not the same prospect as the person who visited your homepage from a branded search and left immediately. Running one retargeting ad to both is a misallocation of budget and a mismatch of message. The cart abandoner needs urgency and social proof. The homepage visitor needs awareness and positioning. A single ad cannot serve both — so it ends up serving neither particularly well.