In fact I think the more you write out for yourself, write on your slides, or try to memorize, the more difficult the presentation becomes.
The practice is more about stumbling a bunch of times. I hate when I repeat the same word or phrase within a few sentences of each other. If I notice that I say the same thing twice on one slide, maybe I'll stand there for a second and think of a new way. The next time I practice through I might use a 3rd way, but at least I'm not repeating.
I only really memorize maybe the first two sentences I'm going to stay just to get the ball rolling smoothly, and maybe a final sentence so my exit is clean.