Initiate Synchronization

The 'Initiate Synchronization' button (present on the integration configuration screen) should be used in cases where you have expanded artifact filters to make new artifacts eligible for synchronization. It will prompt you to select one or more projects to synchronize, and will immediately trigger a special high fidelity full scan*  for the project(s) selected, causing eligible artifacts in those projects to synchronize.

You can learn more here.

*How is this different from a normal high fidelity full scan? This special high fidelity full scan will include all eligible artifacts, rather than only previously synchronized artifacts.

Process All Artifacts

The 'Process All Artifacts' button (present on the Field Flow screen) can be used in cases where you've added a new field mapping to your integration or otherwise would like to force through updates for all artifacts in a collection. Note that this can lead to much higher server load  than the 'Initiate Synchronization' button, as this forces an extra special high fidelity full scan to run that scans ALL artifacts in the collection (regardless of whether they have synchronized or not) and marks all artifacts as 'changed'. In contrast to 'Initiate Synchronization,' this will kick off the high fidelity full scan at the next scheduled change detection interval, rather than immediately. 

You can learn more here.

Summary