You should definitely delete your "mobile advertising ID" (MAID), change it frequently (Android) or prohibit your apps from tracking (iOS) if you do not want the data from different apps to be merged and sold again by so-called data brokers.
More information
If you use iOS or Android, your operating system transmits an advertising ID to your apps in the background. This ID can be attached to the data records of individual apps. If the provider of your apps then sells this data, brokers can merge it with other data sets of yours. This creates veritable stockpiles of your personal data and interests that are traded online.