I have been watching some videos on youtube about interplanetary missions, and I am confused about something. In many of the videos they say that you should take off in a west facing direction (270 degrees) instead of the typical east when visiting inner planets. I have not seen one where they explain why that is better. I know exiting Kerbin's local system in the retrograde direction (from Kerbin's velocity vector) will help visit inner planets because it slows down your orbit with relation to the Sun, but I don't think that leaving Kerbin in a west facing orbit will affect that at all. It just changes the position you need to burn on your orbit to exit Kerbin's system. If I am right, then isn't orbiting west just a waste of fuel since you already have velocity in the east direction from the planet's rotation? Am I mistaken? Thanks for clarification.