The comedians/cruise director/piano player/guitarist etc will change. The Playlist production shows in the main lounge may be the same.
In the past they only changed the Playlist shows out during drydocks, but now that they're basically just screensavers they can be changed out more often.
Given the choice I'd always go on a longer cruise vs a shorter one 🙂 sure the playlist shows may or may not be the same but there's plenty more to do onboard during the showtimes, assuming you don't want to see them again.
Often for longer cruises like 8 day, Carnival will bring on a variety show as well - a one man band, ventriloquist, etc, for one or more nights of entertainment since there are only so many different Playlist Production shows the dancers onboard can perform.