A personal speech coach can help you become more effective at any given time and anywhere. It is important to note that we all have limits as far as our own skills are concerned and that these personal limits are generally not very different from the limits you would face if you were speaking publicly. The same general principles of effective communication apply to speaking in front of an audience: you need to be able to communicate effectively without coming across as arrogant, condescending, or patronizing. If your goal is to truly improve your skills and polish your public speaking skills, then you will benefit from hiring a personal speech coach.
What a speech coach does is challenge your assumptions and encourage you to question them. They will remind you of previous presentations that you might have made and how successful they were. They will encourage, cajole, test, challenge, and improve every aspect of your public speaking skills.