There are two different ways to close apps on Android. And each method has a different purpose.
There is a way to simply close your apps so that they stop using your phone’s memory as much. Your phone will usually run faster and your battery will drain slower as a result of closing your apps this way.
Then, there’s another way you can close your apps via the app manager; this is called force closing or force stopping an app. You should only close an app this way if the app is acting up and it’s unusable in its current state. Force closing an app can sometimes mess with the integrity of the app, so do this sparingly.