When your initiation is all about you - your perspective toward where you are, who you are and/or what you're doing - you establish a solid foundation for your character to move forward from while keeping the door open for many potential paths forward, confidently capitalizing on the improv "magic" of "making it up as you go along."    If instead you dictate the scene to your scene partner(s) - defining their role, their perspective and/or reason for being on stage - you risk putting all the onus for the scene on your idea and pushing the audience in a position of critique rather than of awe.  Saddled with your idea, your scene partner may be hesitant to make a bold move of his/her own, restricting their creativity and hampering the scene's growth potential.