Question: I wanted to know what are advantages and disadvantages of DAG over Blockchain ?

Answer: 
I'm answering on the context of Iota
**Advantages**

1. Best suited for micro-transactions because it's not worth paying someone 0.5$ if transaction fee is 1$.
2. Scales infinitely at least theoretically, as the size of the network increases, the speed increases too.
3. It removes the need for miners, making system more decentralized otherwise large mining pools can take over or influence the network.
4. Iota implementation is also quantum resistant.

**Disadvantages**

1. Needs a lot of traffic before it can start operating.
2. Decrease in network traffic renders network vulnerable to attacks.
3. Coordinators used for kick-starting look fishy to the community.

I'll update as I find more interesting points to add.
Directed Acyclic Graph (DAG) coins. IOTA’s Tangle, Byteball, and Raiblocks are examples. They’re gaining a lot of traction as they seem to be a really awesome alternative to the blockchain.

RaiBlocks uses a block-lattice structure. Each account has its own blockchain (account-chain), equivalent to the account's transaction/balance history. Each account-chain can only be updated by the account's owner; this allows each account-chain to be updated immediately and asynchronously to the rest of the block-lattice, resulting in quick transactions. Since blocks can only be added by each account-chain's owner, transferring funds from one account to another requires two transactions: a send transaction deducting the amount from the sender's balance and a receive transaction adding the amount to the receiving account's balance.

Each individual transaction is a block, and each block is able to be processed instantly by the network. It secures its ledger via delegated proof of stake. They pre-cache the anti-spam Proof of Work for the next transaction once a transaction is sent, making transactions instantaneous, as both sides have the proof of work ready to go.

Instead of each block having many separate transactions, RaiBlocks reduces this by everytime a new tx is formed, it absorbs the tx behind it reducing the size of the block. So rather than having a maze of tx like Bitcoin, RaiBlocks stores the values of accounts instead.