Full nodes typically are computers that synchronize with a blockchain or DLT network in order to store a record of transactions or perform other functions.
On Radix, full nodes are primarily useful for those who want to prepare to become a validator node, or wish to operate a fully trustless connection point to the network for account control or network monitoring, via the Core API.
A full node may easily register as a validator node, meaning they can begin accepting stake and will be considered for being included in the validator set by the network protocol.
Further reading: