More than you think which is why you must take GDPR seriously. The big prize for those that do this well is the trust customers have which will be rewarded in lifetime revenues.
And the ability to access and analyse all that unstructured data that has high potential value but is not analysed at present. See "GDPR a catalyst to better analytics?"
The surveys imply that people will welcome the increased control of their data that the GDPR provides to them, and will actively leverage their rights. Organizations should take this into consideration when prioritising solutions and business processes around data subjects’ rights amongst all their GDPR priorities. The good news is that progress on personal data management will most likely be well received within your customer base–and those who offer better services are more likely to win the trust, and hence loyalty, of many Europeans.