These app closing systems have some pros and cons, depending on the scenario and device you have.
Greenify or app optimisation is very useful in 1GB or less RAM smartphones, but if its 1.5 GB or more RAM, then its not required in most cases. However, there are some exceptions where they are very useful, like when the app running in background is not functioning well.
These systems close the apps, and when you open it next time, app has to open from the beginning which stresses CPU, takes more time to open app and impact battery timings. So it decreases responsiveness and battery timings of smartphone in most cases.