In Star Wars: The Old Republic, while characters from both sides will visit the same planets, they generally do so at different level brackets and visit different areas in those worlds. For example, playing on a PvE server I haven't come across any players of the other faction just doing my world quests -- only if I go out of my way to explore planets will I occasionally catch a glimpse an 'enemy' player.
I'm curious if this is a result of "phasing", and so such things don't happen on PvP servers, or if it is just how the wolrds are designed... and if the latter, then how much difference does being on a PvP server actually make?