Choosing Snapshot vs Duplicate depends on whether your project timeline contains multicamera clips and compound clips. Snapshots will preserve those instances as they are in the project/ Duplicate will reference the originals.
So later if you make changes to the compounds/multicams after a Snapshot- the snapshot version will not reflect those changes while a duplicate will. More details here:
https://support.apple.com/kb/PH15846?locale=en_US
Noah
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