The main purpose of assetlinks.json is to enable Android App Links. This allows for a seamless user experience where clicking a link to your website directly opens the corresponding content within your Android app, rather than opening it in a web browser.
assetlinks.json is a vital component for any Android app that wants to provide a truly integrated and seamless experience for users interacting with its associated website.

All node access modules are queried using hook_node_grants() to assemble a list of "grant IDs" for the user.
This list is compared against the table. 
If any row contains the node ID in question (or 0, which stands for "all nodes"), one of the grant IDs returned, and a value of TRUE for the operation in question, then access is granted. 
Note that this table is a list of grants; any matching row is sufficient to grant access to the node.

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