There are some benefits on using xml reports instead of exec-files

1. no dependency of jacoco.jar needed, so reports will be always actual no matter what jacoco version created them (currently reports created by newer version of jacoco do not take any effect because jacoco-plugin's dependency is older);
2. xml report contains all the information needed not to lose in the functionality of the plugin; report contains class, package, method coverage and their name - everything that is necessary for the plugin to work;
3. in case of xml report - this report can be generated by the build tool or even by the jacoco's cli giving user more flexibility in configuring his build pipeline
4. xml reports from any other coverage tools (scoverage, cobertura, etc.) can be easily converted into jacoco's xml format and get all the benefits of this plugin (reporting, dashboard views, etc.)