I have @firehose on my instance. It doesn't seem to take up excessive resources, but my instance is a small one, and @firehose doesn't exhaustively follow everyone. I intended it to get replies in conversations for those people I don't want to follow myself (eg. those who primarily speak a language I don't, but sometimes have interesting conversations in English). But it doesn't work as well as I'd like, and I haven't been maintaining its subscription list very well.