What Is Blockchain snapshot?
A chain snapshot is a dump of the chain state. By downloading the snapsnot a new blockchain node can sync faster to the chain tip, instead of downloading each block and verifying each transaction individually from the peer-to-peer network.
The snapshot may be
Chain built-in sync mechanism: Ethereum Snapshot Protocol (SNAP)
Manually hosted snapshot: Polygon manually hosted snapshot downloads
Different snapshots offer different security guarantees. For example, when downloading a snapshot from a Polygon manually hosted snapshot repository, you trust that the admins of this repository have not modified the current historical blockchain state. The built-in Ethereum Snapshot Protocol verifies from the peer-to-peer network that the snap state is correct.
How much snapshot speeds up the node sync depends on what kind of node you want to run: full node without event history, a full node with event history or archive node. For example, even with a snapshot syncing a BNB Chain full node with event history will take several weeks, because Erigon needs to construct the historical events from the raw blocks after the download, as historical events are not precomputed in the snapshot.