The switch or the ceiling rose can double as a junction box, which means if the switch is used you need a deeper back box and the neutral is taken to back box, and there is no permanent line at the light, so precludes the use of emergency lights and fans at ceiling rose location. It also increased volt drop as often the wires need to run further, but with modern lighting volt drop is not really a problem.
If the ceiling rose is used, it means no neutral at the switch, so electronic switches can have problems with flicker with LED lighting and flashing when switched off as some power has to go through bulb to power switch, this is not a problem when the electronic switch is provided with a neutral.
The use of non British lights and fittings where switches need a neutral or the lights have no felicity for the loop has seen a move to using the back box as a junction box, however unlike the ceiling rose there is not a ready built set of terminals to enable wiring.
The biggest problem is the lack of sleeving on wires, in the days when it was red and black cables we had special twin and earth with two reds, but with colour change this seems to be rare and the blue is sleeved with brown, which often in either not fitted or has fallen off, so we see a black or blue wire which is line not neutral, so many errors are made, so what ever you do take photos and use tape to show which wire is what.
I first read your post and thought wrong, likely 9 or more wires, but I think when you say wires you mean cables? And yes three cables at the switch when switch is used as junction box, and three cables at ceiling rose when that is used as junction box, unless last one in the circuit. There will be exceptions to this when spurs/branches are taken to other lights, or you have two way switching.
