Android凌空图书馆，在哪里使用，哪里不去

As our typical old asynctask network connection is getting replaced by volley. It's fast as I have used so I know. I downloaded images and showed. When I again restarted the app it didn't take time to download. So is it caching images for sometime ? And as it is recommended not to use in heavy download, any reason ? Or it is the reason that it keeps images and all in memory ? I saw I/O video of volley. But I need clear explanation. ThanksAs our typical old asynctask network connection