Being a DHT server → contributing to the DHT network health and storing of records
Being a DHT client → using the DHT to do things like advertise and discover content (sometimes called Put/Get of Provider Records)
So there’s no reason a browser should benefit from being a DHT server, and ultimately given the low uptime of browser nodes (e.g. a tab closing killing the node) it’s likely unhelpful to the network as well and so shouldn’t be enabled.