If you want your presentation to sound like, look like and be like every other speech, training, class or workshop, then only put a little bit of effort into preparing.
If you want to separate yourself from the rest and have greater impact, an authentic performance, more creativity, fresher ideas and a remarkable presentation, invest more time on the front end.
Never settle for your first ideas. They are just the seeds to more authentic-rich ideas. It is funny how long it takes and how much preparation goes into being an authentic presenter.