We mostly use rollup to publish package onto NPM. For most all other use cases, we use the Meteor build tool (probably 99% of the time) for publishing packages. If you're using Node on FHIR you probably won't need to know rollup, unless you are somehow working on helping us publish front end user interface components using FHIR. That being said, we have been migrating away from Atmosphere package manager towards NPM. As we continue to migrate away, we may publish other NPM packages using rollup.