The need for writing a script for your presentation as part of your preparation is depended on some factors. For most people it would be best to script, but it may not be a good solution for everyone. Whether or not you script your presentation the end result should be similar.
If you do not script your presentation, you may need more rehearsal sessions to get to a high quality presentation. If you do script your presentation you may find the rest of your preparation phase to go faster. Some are getting more comfortable if they have written a script as part of the preparation, others may get more nervous from knowing that there is a script. Whether or not you have written as script, for your audience there should not be a noticeable difference if you prepare correctly for your presentation. Reference is made to the book that is part of the Public Speaking Kit for various tips about the best preparation for your next presentation.