The full node is considered backbone of cryptocurrency blockchain while light node only provides ease of use. The light node does not store complete blockchain, instead it only store block headers to validate the genuineness of transactions. The lightweight nodes use Simplified Payment Verification method to verify transactions. As compare to full node, the lightweight nodes are easy to run and maintain. The light node depends on full nodes to connect with bitcoin network.
There are few downsides of light node that users should be aware of. It does not authenticate instructions of bitcoin. The light node wallet happily accept invalid or fake bitcoins and the user will be left out of pocket. Lightweight node also send private keys and addresses to third party. It allows the third party users to spy users past and future transactions. Full node avoid suck kind of spy by third party users by downloading the complete blockchain and scanning it locally. The light node also not follows security steps which leave the user vulnerable. The best example is 4th July 2015 Accidental Chain Fork where full node were unaffected while light node were in danger.