If you play Starcraft 2 against your friends or on the Battle.net ladder, then you want to win more games right? Since Starcraft 2 is all about economy and macro, the more you can damage your opponents while building yours the better. You can use Medivacs to destroy your opponents economy while you build yours up and take the lead.
Medivacs alone probably won’t win you many games. They have to be used in a smart way to catch your opponent off guard to do the most damage possible. One of the best ways to hamper your enemy’s economy is to drop a group of Marines into his mineral line and kill off as many workers as possible.
As long as you have good macro, you’ll be able to pull ahead and stay in the lead economically. Which means you’ll be able to have more resources and build a bigger army to crush him in the end. But instead of just flying a Medivac full of Marines into his base at random, it’s best to use them at key times to hurt him the most.
First off, Medivacs are a great way to counter attack. If you get attacked by the opposing player, his army will be in or near your base. When you drop a Medivac full of Marines into his base he will have to find some way to deal with it or just lose his whole base. This usually means pulling back his army which will take the pressure off of you.
Many times your opponent won’t notice right away since they are in a heated battle, and your Marines can freely do damage, which can be devastating to his base. As long as you survive the attack on your base, you’ll be in a great position to pull ahead in army size and take the win with superior numbers.
But since your Medivacs will be doing mostly economic damage you need to be sure you’re doing your best to macro effectively so you actually take the lead by a good margin. It won’t do you any good to destroy his economy if you forget to build up your own.