Well the advantage of batch production is that the company that uses it has a variety of products rather than just one type so therefore it gives customer a larger choice and hence a larger possibility of sales. Another advantage is that the company is reducing its risk on simply concentrating on one product; it produces a variety of different ones of the same type.
The main disadvantage of batch production is that there's a period of time for which the machinery is being changed and this causes the productivity to stop completely which the could cause the workers to sit idle; basically the work stops.
The advantage of flow production is that the company using it can mass produce many items at once which would would reduce the unit cost, hence reducing the price and possibly increasing sales. It may therefore develop a good brand name for low prices.
The main disadvantage is that the work is quite repetitive for workers and can cause demotivation (imagine sitting at a conveyor belt all day tightening the same screw!) which leads to a poor quality/productivity. Also opposite to batch production, the company is only producign one type of product therefore it's concentrating all of its risk on one good.