Yes, depending on one's preferences (which can be changed, whenever the need arises, per activated process if desired), and it runs automatically in the background. To give you an idea, when on 'AutoSense', I currently have 2071 MB of the total 8000 MB RAM in use (Photoshop open with one 21MB image, video in the background, browsing 10 websites, and having several Explorer windows open to move files, and the virus scanner is probably doing its background tasks, as are a number of other processes). Photoshop has plenty of RAM available for Scratch when needed, before the efficiency drops below 100%.
Cheers,
Bart