If the room is square this is obviously not an issue but in a rectangular room there are a few issues that need to be addressed.
One customer had a room where the ceiling was 4m long but only 1m wide and wondered which way was correct - as the panels can be installed either way it's a personal taste issue rather than a right/wrong way.
If you are using a flush fitting panel, such as Labo or Blanca it is not going to make much difference as the joints are not that visible. If you are using the cladding with the infill strip or using a v-groove panel such as Topline then the direction will have more of an effect, but not a massive one.
Running the ceiling panels along the room will have the effect of making the room look longer and narrower. Running them across the room will have the effect of making the room look shorter and wider.
So it really depends which you prefer. If you do choose to opt for cutting the panels shorter you will find it is much easier to fit, cut and handle smaller lengths. Also it might well be that you will require less panelling to cover the bathroom ceiling in one direction than it will in the other.
