I've googled a lot about X button, that doesn't quit app, but simply close the window andnd haven't found a clear answer. I want to be able to know if open apps affect battery life or other resources.
Should I quit apps or close windows, letting apps work in background?
Best Answer
One of Mac's most confusing features is the red close button, which you think would shut down an application but often doesn't. When you press X button in the window - you actually close the windows related to the app, but it does not quit. Here's more information from Apple's support pages:
If you want to quit the app (release the memory, reduce CPU usage, etc) then there are several ways to do this:
Quit
option.Applications
>Utilities
>Activity Monitor
.You may also want to overload the default behaviour, and to make it like in Windows OS, but you need to use separate utilities (like RedQuits). There are a bunch of those utilities that close applications when you click the the red close button.
In overall, to answer your question about how it hits system efficiency, memory and battery: OS X handles it properly and does as much as possible to optimize efficiency, unless the Application itself is written poorly. OS X internally has a lot of optimisations like App Nap which help to keep background apps' effect on system resources to a minimum: