Maximal Extractable Value (MEV) refers to the maximum amount of value a blockchain miner or validator can make by including, excluding, or changing the order of transactions during the block production process.

1. Inclusion of Transactions 

- Validators will have a right to select transactions to appear in a block. It might favour those transactions with higher fees, or adhering to specific patterns that cause some extra value.

2. Exclusion of Transactions 

-  Without including particular transactions, a validator can manipulate the market, whereby a trade can be delayed to capture profit from price movements.

3. Transaction Reordering 

- Transactions within a block can be reordered by validators. This reordering enables profitable practices such as front-running and back-running.

1. Front-running 

-  A front-run trade entails block producers and searchers inserting a buy order before a similar order is executed. 

- They benefit from the impact the other trade has on the price.

2. Back-running 

- A back-run trade occurs when a target trade is immediately succeeded by that of an MEV actor. 

- The MEV actor benefits by capturing a large portion of liquidity in a DEX and selling the asset at a higher price.

3. Sandwich attack 

- A sandwich attack entails organizing transactions to execute a buy order before and a sell order after a target transaction. 

- The network participant gains from the slippage of the original trade.

4. Liquidation 

-  DeFi protocols depend on MEV to liquidate the positions of borrowers when their collateral goes below the set threshold. Since the liquidation needs a faster response, MEV actors pay higher fees for priority. A portion of the fees goes to the MEV actor who facilitated the liquidation.

1. Network security

MEV incentivizes miners and validators to secure the network by offering additional profit opportunities. 

2.Market efficiency

- Arbitrage opportunities within MEV can help balance prices across different exchanges. 

1. Higher transaction fees

- Competition for MEV drives up gas fees, especially on networks like Ethereum. As miners prioritize transactions with higher fees to maximize extractable value, regular users face increased costs for processing their transactions.

2. Unfairness

-  MEV creates an environment where sophisticated actors with advanced tools and knowledge have an advantage in capturing value. Leading to an imbalance because ordinary users lack the resources to compete effectively.

3. Network congestion

-  MEV-driven activity can overload the network as actors flood the blockchain with transactions to capture opportunities. 

- Such congestion slows down transaction processing times and reduces the efficiency and usability of the network.