Depends on the station, the timeslot, and the type of show — something on a bottom-tier network that gets ratings near top-network quality would be great for that show, but a death-knell to a show on a top network. Most shows in the Top 30-40 could be said to be doing very well, with the Top 20 being major hits. There have been shows, however, that were cancelled for not getting high ENOUGH ratings (like the "NBC Must-See TV" Thursday line-up having a string of cancelled series that got Top 20 ratings, but still a HUGE drop-off from "Friends" and "Seinfeld", both of which sandwiched the shows).