Long: In most instances the disadvantages greatly outweigh any advantages when you memorize a speech.

Look at what you don’t achieve when you memorize a speech –

You’re can’t easily respond to audience reactions to your message.
You’re focused on the Speech, the next word or phrase rather than on your audience.
You’re so buried in the Speech, You can’t make effective eye-contact with the audience.
What happens if you lose your place? Do you apologize? Do You begin again…from what point?
You can’t walk around the stage or the front of the room. If you look where you’re going you may lose your place in the Speech, and if you don’t look where you’re going…Disaster.
You risk losing the attention of the audience.
Without connecting to your audience you’ll never build Trust with the audience and one of the main reasons to make a speech or presentation in person is to build a personal connection that lays the foundation of “Trust”.
Actors & other performers study for years or a lifetime, to learn how to deliver lines Naturally. Are you that well Trained, Practiced, and Polished?
Speakers learn solid Speaking Techniques which builds Confidence. They become effective through Practice, success follows and the entire process can be short if you honestly put in some effort.