Yes this is related to Horizon: High Context Topic Cards, the original thought was that we need to expose this setting so people can turn on excerpts in those Horizon topic cards without console access… but it’s a little bit of a dangerous setting to expose because if you enable it you add a lot of data to the topic list even if excerpts aren’t being shown in the current theme.
The follow-up is to instead enable the hidden site setting when the Horizon theme has topic card high context enabled… that way the setting is constrained to a situation where it will be used.