  Large-scale quantitative analyses have shown that individuals frequently talk
to each other about similar things in different online spaces. Why do these
overlapping communities exist? We provide an answer grounded in the analysis of
20 interviews with active participants in clusters of highly related
subreddits. Within a broad topical area, there are a diversity of benefits an
online community can confer. These include (a) specific information and
discussion, (b) socialization with similar others, and (c) attention from the
largest possible audience. A single community cannot meet all three needs. Our
findings suggest that topical areas within an online community platform tend to
become populated by groups of specialized communities with diverse sizes,
topical boundaries, and rules. Compared with any single community, such systems
of overlapping communities are able to provide a greater range of benefits.
