From the resource:
This is the second in a series of posts which constitute a “lit review” of sorts, documenting the range of methods scholars are using to compute the distribution of topics over time.
Graphs of topic prevalence over time are some of the most ubiquitous in digital humanities discussions of topic modeling. They are used as a mechanism for identifying spikes in discourse and for depicting the relationship between the various discourses in a corpus.
Read more here.