Bitcoin checks and balances When a new block is created, does each block need to be validated?
How does it differ from validating transactions?

Why miners would waste time validating transactions and blocks when they could spend their time mining
Why miners would waste time validating transactions and blocks when they could spend their time mining?


When a miner successfully mines a block, they  transmit the block across the network. As the block starts to ripple out across the network, each full node receives a copy of the block and after validating it they add the block to the existing chain. Now consider a situation, where the block that is mined does not meet the consensus rules. As the full nodes receive the block, they validate the block to ensure it meets the validation criteria and if the block is invalid, the full nodes will reject the block and will not transmit it further. Thus those miners that do not satisfy the consensus rules will have their block rejected, and will lose their block reward and the effort they put in to mine the block. 


  When a new block is created, does each block need to be validated? How does it differ from validating transactions?


When the full nodes receive the block, each node performs a series of checks to ensure that the block conforms to the consensus rules. Similarly, when a transaction is broadcasted, each full node receiving a transaction will perform checks before including it in the mempool. If the transaction is invalid, the transaction will be rejected and will not be broadcasted further by that node. All the transactions included in the block being valid, is a subset of the block verification criteria. You can refer the bitcoin wiki page here to get a checklist on the transaction and block validation.