Removing the default exclusions may have a severe impact on your database both in terms of load and for growth. There can be a significant increase on the load on your agents that are installed on your domain controllers as well. This will also result in an increased amount of traffic from the agents to the coordinator and then from the coordinator to the database.
The DCs may become slower in terms of responsiveness. The amount of impact completely depends on your environment, however these objects have been excluded by default due to the known amount of excessive traffic and noise they can cause in regards to AD Queries.