The two best advantages of boot is simplified & version conflict free dependency management through the starter POMs and opinionated auto-configuration of most commonly used libraries and behaviors.
The embedded jars enables to package the web applications as jar file which can be run anywhere.
It’s actuator module provides HTTP endpoints to access application internals like detailed metrics, application inner working, health status, etc.
On disadvantages side, they are very few. Still many developers may see the transitive dependencies included with starter poms as burden to deployment packaging.
Also, it’s auto-configuration feature may enable many such features which we may never use in application lifecycle and they will sit there all the time initialized and fully configured. It may cause some un-necessary resource utilization.