They only add a single extra dependency, so not really much value. Fixes gh-770
Flyway starts up with its default settings if it is on the classpath. You can also ask Boot to barf if the migration scripts are missing. Fixes gh-730
If Liquibase is on the classpath it will fire up on startup. Various config options are available (as well as the option to disable it). Liquibase uses a YAML format for changes (in classpath:db/changelog).