Roundups group related topics so the board can show structure instead of isolated spikes. They help you see whether movement is part of a neighborhood or just one small page flickering alone.
A topic board becomes more useful when it explains neighbors. Roundups make that visible by grouping tags and then surfacing the posts and profiles most responsible for the cluster.
Use roundups when you want a broader read before drilling into a single topic. They are better orientation pages than raw tag archives.