Well the first answer is, just about anything!!! Remember that AC's can have a single placement point (they don't need multiples) meaning that the family will behave very similar to placing any non-hosted family. I'll let Krista follow-up with a post on this brilliant work-flow, including my suggestion on how to "circumnavigate" the issue of limited category options for AC's.
On to the main subject of this post....
Since time eternal (or at least as long as I can remember) Revit has had a 1D array (ie, define a start point an end point and elements are arrayed between them). However in architecture there are certainly a number of occasions where a 2D array would be far more useful (ie create a "grid" of elements rather then a single row). Now this little technique will not solve all problems, but it may help with some, and inspire others.
My use case is this, we do a number of education facilities at our firm, which means classrooms, classrooms often means regulated "arrays" of chairs or desks, rows and rows of them in fact. So what if we could simple define the outside corners of where we want our furniture, the distance between each row and column, and let the computer do the rest, including dynamically updated if we change the size, interested!?
Now that we have our armature, we need some panels to go in our grid. Time for a new family, this time a Panel by Points family (also can be put into the Furniture Category). This family is a little more complicated, you could model your actual furniture here, but my suggestion is to load a family built from the standard template(s). The trick is locating the family in the panel. Here, I've created two sets of crossing reference lines that lock my tablet arm chair to the center of the panel. You could always look at doing an offset, or something else, but for the purposes of demonstration, I decided to keep it "simple".
As with just about anything that uses Adaptive Components, more CPU power is going to be your friend. Regen times can be high with Adaptive Components, though as long as the nested family is not too complex, you should not see anything to far out of the ballpark here.