LeadPages is *not* the same thing as your email marketing software, such as Mailchimp, ConvertKit, or Infusionsoft. LeadPages helps you get more subscribers, but does not allow you to send regular emails to your list. So, LeadPages can be used to grow your email list and then you can use another service to communicate with that list. Make sense? In that case, why would someone want to use LeadPages? Because they offer tons of templates to help you make high-converting landing pages and allow you to easily send content upgrades.
Prospecting and marketing are all the things you do to get people into the first of your sales funnel stages. Note that stages are broken into two or more steps wherever possible. A demo could be called a single stage, but in real life it involves a lot of things: contacting the customer, sending reminders, doing the demo, and then following up. Whatever your own sales stages look like, the support you need in managing them will be the same.