2 things came to mind:
1. it'd be cool if a whole instance could set a default opt-out. (it'd also be cool if single users of that instance could still opt in, but that's less important.)
2. I can imagine disabling "search engine" indexing but still wanting to opt in to Holos Discover: if I don't want to be on web search engines but do want to be on ActivityPub-native search engines. this is a limit of the profile option granularity, but as an interactive bot, Holos could work around it…