What does ActiveDock do that the default Dock doesn’t? For starters, it gives you window previews that make it easy to identify open apps while switching between them. But it doesn’t stop there. It allows you to resize windows to different preset sizes right from an app’s preview.
The Show/Hide Desktop dock icon is also a nice touch, and a pretty useful one too!
ActiveDock allows you to group disparate items into a single view. This comes in handy when you want to, say, keep all the resources relevant to a particular project accessible from the dock. You can add apps, files, folders, and photos—any item works as long as it’s accessible via Finder. (If you want to group non-Finder resources, consider apps that let you create unified workspaces.)
You can’t create such groups with the macOS Dock easily. You’ll first have to move/copy individual Finder items out of their original location to a separate folder. Then you’ll have to drag that folder out to the Dock. That’s not convenient at all.