Any need for coinbase field in coinbase transaction?
The coinbase field is crucial for pooled mining. All workers in a pool will be working to produce a block with the same list of transactions and the same block reward recipient address (that belongs to the pool owner/admin). The "nonce" field in the block header is only 32 bits long. The only way each worker can independently avoid wasting cycles on duplicate work is for the each worker to be assigned a different piece of coinbase data.