You are an actor and your job is to become a character, not merely to recite lines of the character. You want to suspend reality for a period and transport the audience to the world depicted on the stage or screen; you want them to become a part of the fantasy world you and your fellow actors and directors and producers and crew are creating. You no longer exist. The world of the audience no longer exists. What exists is the world of your play or movie, and the characters contained within. This is the goal.
When self-tape auditioning, you are attempting to show the director and producer that you possess the skills necessary to abandon self and fully and completely become the character in their production. You will always give a more convincing performance, and that is precisely what an audition is, by performing off-book when possible, and the only way to do that is to fully and completely memorize your lines.
Memorizing Lines Allows For Deeper Character Development
To give a convincing self-tape audition you must do more than just perform a character, you must become the character. Movement, voice inflection, dialect, attitude are all part and parcel of your transformation. You cannot do that to the best of your ability if you are uncertain what your next sentence is.
Memorizing Lines Allows You To Converse
When the curtain comes up or the director announces "action," soon thereafter you will, in most cases, interact with another character on stage. You will have a conversation and your job is to make that conversation appear real and free. Many self-tape auditions likewise require interaction with another character and you, of course, will want to submit an audition self-tape that a director or producer believes fits in the production. Knowing ahead of time what you are going to say enhances your ability to converse convincingly in character.
Memorizing Lines Allows You To Maintain Proper Eyeline
Many have written a good deal about the need to maintain proper eyeline during self-taped auditions. For this discussion understand that it is never good to look directly into the camera, a focus slightly off-camera always presents better. Having your lines memorized allows you to be 100% off-book, keeps your eyes from dropping, adds confidence, and frees your eyes, enhancing your ability to give a commanding
The above pertains to self-tape auditions that are not specifically identified as "on-book," of course. You should always follow all audition instructions. And you should not take from this discussion the belief that "on-book" auditions or reading is bad, just the opposite. Cold reading skills are essential for any professional actor and you should give attention to developing them.
Prepare, memorize, and good luck on all of your self-tape auditions.