In my experience, it varies. If your electrics are all nice then there'll just be a few wires to connect up and that will be that. If things aren't going nicely then you'll just have three terminals on your new light (live, neutral and earth) but a load of extra loop wires that somehow need to be connected even though your new rose doesn't have the terminals. (And obviously the inbetween position where you have a load of extra loop wires but your new ceiling roses actually has all the terminals to make it easy.)
In my experience, it varies. If your electrics are all nice then there'll just be a few wires to connect up and that will be that. If things aren't going nicely then you'll just have three terminals on your new light (live, neutral and earth) but a load of extra loop wires that somehow need to be connected even though your new rose doesn't have the terminals. (And obviously the inbetween position where you have a load of extra loop wires but your new ceiling roses actually has all the terminals to make it easy.)