For a route matching multicast destinations, this controls whether that multicast traffic is actually forwarded or explicitly filtered/dropped; per the field's own description this setting is simply not applicable for an ordinary unicast route. An admin would only need to touch this when defining a route for a multicast address range that should specifically be blocked from crossing the bandwidth-constrained satellite link. For example, setting this to filtered(2) on a route covering an unwanted multicast video feed keeps that traffic from ever consuming satellite bandwidth heading to a site that doesn't need it.