Interested Services means the prospective service that your contact may take in the coming future. This can also be the service that your client has yet to decide to go ahead with.
The Interested service will give you and your team members an idea about the future interests of your contact and act accordingly during a consultation. It also helps in creating various marketing campaigns based on their preferred interested services. In short, opportunities are the provided service your clients are interested in but are yet to decide to proceed as an application.