If you sell consumer products via the web, then you know that once you sell a large item that consumers need, they won't be buying that item again very soon. So once you've sold the first digital camera to a consumer, your recommendation engine should know not to waste time trying to get them to buy another one. The salesperson is trying to determine the profile of the potential customer to know what products to recommend and the likelihood of purchase. The same holds true on an e-commerce site where a customer's purchase history should be reflected in his or her profile in order to make the best possible recommendations. Having made a particular purchase is not the only thing that causes a person's profile to change.
Interests change from time to time, and that leads to regular customers becoming former customers.
If a customer who used to buy hiking equipment from you is now interested in camping or boating equipment, your site needs to quickly recognize this change and adjust their profiles to keep in step. Profiles can even change when a product is never purchased. Potential vendor's sites are visited, and web site profiles are created to recommend the right product. When a project is delayed or canceled, the vendor web sites don't know that the window of opportunity to sell to that prospect has closed. Later, when the member of the evaluation team returns to a vendor's site on a different mission the interest profile is out of date, so there must be a way for the prospect to update his or her interest profile.