New in R398.2 is the Instance Bar, a new way to view and organize all the instances in a layout. Next, a short description about some of the features off the top of my head.
Hierarchies
One of the bar's primary objectives is to help visualize and build complex hierarchies, which can get a little bit tedious and confusing just by using the layout view. Hierarchies can be made by dragging and dropping tree items on top of each other and also by dragging an instance from the layout view into the Instance Bar.
Folders
The other main feature is that now there is a way to organize instances in a folder structure which is independent of how they look in the layout and has no impact at runtime.
Additional Information
A secondary feature is showing, in a compact way, information which was previously not easy to see at a glance. By left clicking on the bottom of the bar or right clicking anywhere else, you can bring up a context menu option called "Show more information for", to toggle additional information about each instance, such as if they are a template or belong to a timeline among a few others. This was done like this because there is quite a bit of this instance specific information and showing it all at the same time could become messy very quickly.
Search
The search bar at the top of the bar can be used to search by the display name of items, if there is no match with the display name though, the search will also attempt to match, with the object type name, the plugin name or any tags an instance might have. Typing a layer name will filter the tree to show only the instances in that layer.
Additionally there are a couple of "special" search terms. Typing "mesh" (or the translated name if you are not using C3 in English) will search for all the meshes in the layout. Something similar happens with the word "hierarchy", which filters the tree to show only the root level hierarchies.
Tags
The bar also has a minor integration with the new Tags feature. Any instance which has tags will show the first tag as it's display name instead of the object type name which is shown by default. The other tags can still be used in the search bar though!
Global layers
There are a couple of features which are not obvious and they have to do with how the bar displays instances coming from global layers. If any, these instances are also shown, but in a slightly different way because as it turns out, showing them like any other instance caused some problems. When toggling the "Layers & Layouts" options, an icon will be shown next to global instances to quickly identify them.
Under certain conditions, items in the tree might become highlighted in red. This cases are tied to global layers. Since it's possible to make hierarchies from instances in a local layer to instances in a global layer, it is possible for an instance to show up in hierarchy, but be no where to be seen, those instances will be highlighted and toggling the "Layers & Layouts" options will tell you a little bit more information about what is happening.
Another edge case caused by global layers is that a hierarchy might only be shown partially, because the rest of it comes from another layout, that case is highlighted as well.
Performance
Due to an initial bone headed implementation the bar is quite sluggish when a layout has a lot of instances. That is already being fixed.
I think that's all about it. If you have any feedback or have already written some elsewhere, it is a good idea to put it in here so everything is in the same place.