It varies, but as the article says it can be used for things like drug discovery. Imagine there's a new virus running rampant. It works by using a very specific

It varies, but as the article says it can be used for things like drug discovery. Imagine there's a new virus running rampant. It works by using a very specific protein to latch onto a cells so it can pull itself in. You would like to develop a drug to stop it doing that and one way to do that is to find a protein that wants to strongly latch on to an important part of the virus. If it's holding onto the virus the virus probably won't be able to penetrate cells because you're engineered protein will get in the way. This is part of how antibodies work to stop viral infections naturally