Defining success metrics allows you to formulate a game plan for your meetings with prospective clients.
If you know what you need to accomplish, the roadmap becomes very clear for what you need to achieve. If your success metric is defined as your having a comprehensive picture of their challenges with their current provider, you can prepare questions that will expose their challenges. If your success metric is to gather all the data needed to put together a pricing proposal, the game plan is to ask all questions needed to craft a solution for this prospect.
From a prospect's point of view, they have no time or tolerance for salespeople who show up on their doorstep and ask pointless questions for an hour. They are busy and very sensitive about their time. If they accept a meeting with a salesperson, they expect that salesperson to arrive having done their homework on their company and with a laser focus approach to the meeting.
Remember, sales are a profession. They expect a professional experience.