I've managed several User Experience (UX) teams both large and small at Microsoft, and I'm often asked to give feedback on User Interface designs and there is one concept (among many) I frequently stress:
Understanding how the experience scales in response to the number of entities.
Entities in this sense are the concepts the UX promotes: “photos”, “contacts”, “videos”, “likes”
Scaling is not about how the experience is transformed as the number of entities grows and the consequent impact on the user.
The count of interfaces I've seen that are too tightly designed for a “magic number” of entities is staggering. By this I mean, that the design mock ups while extremely beautiful and functional don't take into account what the user will have to deal with: Two few entities or more frequently too many.
Here's a great example from the VLC media player that I encountered today and inspired me to right this post. (FYI am a huge fan and use VLC every day)
Let's launch it, and click Media > Open File.
The following dialog will appear.
VLC is known for supporting many media formats (https://www.youtube.com/watch?v=pRIaU172aKM). Let's see how many by clicking on the Media Files dropdown (located above the Open and Cancel buttons)
Click on the image to see the fill thing.
Fortunately I have a two-monitor system because the width of that thing is 2545 pixels!
How to catch these issues before they appear
I try to evaluate of any UX that shows entities under the following heuristic.
Ask your designers what happens when the user encounters these numbers of entities:
At the very least, you'll force a discussion about what a user is likely to encounter and be more mindful about what your UX designs are optimized for.
Besides the visual layout, it's also useful in helping UX developers pick the right way of implementing the experience.