Older versions of RapidWeaver had issues storing and managing resources. RW8 reworked that process.
Warehoused is RapidWeaver slang for storing and managing resources on a web server manually(outside of RW). Many old time RW users adapted using “warehoused” images to get around the older (pre RW8) resource issues. It also has advantages in being able to add/change images outside of RW.
Stacks 4 introduced a new stack called “site images”. This only works with Rw8 and the reworked resource manager. This allows you to “drag and drop” images into a stacks page once and reuse the same image in multiple places. This is the new default image stack for stacks pages. The “regular” image stack is the old style (pre stacks 4 and RW8) image stack, it’s there mostly for backwards compatibility, but has some edit features that aren’t in the new “site image” stack.
From a published performance side, any image you put on a website is a separate html entity. If you drag and drop the image onto a RW page, it will still be a separate <img> html element when you publish your site. If the same image is used on more than one place then the new site image or warehoused images could be faster as they would be read from the browsers cache the second time.
Edit and Preview should be faster using the new site image stack over warehoused. Site images are stored locally on the hard drive within the project file were warehoused images will need to be loaded over the internet.