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The distributed database and the ability for dapps to share their dapp data with one another are two functions that come to mind right away. Probably also can help with the indexing (as I understand, you can use HAF to build a database for yourself, it helps you with getting the blockchain data you need AND you can add any other data you need, like from other dapps or blockchains, and obviously you can index all of this however you want). I'm sure there's more. The devs can give a listen to @blocktrades going over some of what HAF will provide, the interview is at the link I posted above.

yes, for sure, im also sure that this is just the tip of the iceberg :)