I searched in Cardano docs but couldn't find much related to the BFT node and how it works. And how it is used in consensus. Why is it needed? Any insights would be great. Thanks.
BFT? Do you mean OBFT (Ouroboros Byzantine Fault Tolerant)?
OBFT was the consensus mechanism used on the Cardano network towards the end of the Byron era. Block production in the Byron era was not decentralized as all blocks were created by a small set of nodes run by IOHK/IOG.
The Shelley era (which started in 2020) dropped OBFT in favor of a fully decentralized Oroborous concensus mechanism.
While OBFT is no longer used by the Cardano network, OBFT may be useful for private permissioned blockchains.