Vertical or Horizontal Writing?

Whilst watching Japanese trailers for films and programmes, i have noticed that sometimes the text is written vertically in columns and sometimes horizonatally in rows....i was just wondering why is the text sometimes horizontal and sometimes vertical? Is it to do with the length of the passage of text?

Chihiro-san!

It is only a metter of convenience. They will write either way, whichever direction has more space. There is no "deeper meaning" to be read into it.