Mystery Wiring

I decided to swap my bedroom light fitting. Although I am no electrician, I can manage like for like - or so I thought! I manage to disconnect the old light fitting easily enough. However I was then left with 4 cables poking through the ceiling - four! Having perused wiring diagrams on google it seems to me there should be 2. I cam also see why there might ne 3 but am completely baffled as to why there would be 4! So I gave up and left I for my long suffering builder to sort out and went for a shower - hmmmm seems we have no bathroom light anymore. We habe the answer to the mystery 4th cable. Good thing we have plenty of lamps!