Collections and Favorites (of all these tabs I want all of them)
The idea of these is that you want to save a set of tabs outside the normal opening and closing of tabs so that they are sort of safe or protected from losing them. Collections differs from favorites in that the tabs are not so important individually and can be saved on mass. An important aspect is that tab saving is somewhat permanent, removing tabs has to be done manually.
Workspaces and Tab Set Aside (of all these tabs I want at least one of them)
The Idea of workspaces and tab set aside is that you cannot be bothered to know what tabs are important and which are not at the moment and want to "set them aside" for now. No tab is important enough to have a permanent safe place but at least one of them is probably important. Tabs can be added and (more importantly) removed on a whim without manually removing it from its group (just closing a tab)
please do not use one of these as a replacement of the other. While technically both "save tabs" they are completely opposite in their use.