What is the difference between connecting Slack and connecting Slack Business Analytics?

Slack Business Analytics - This is only for Slack Business users, and will offer a number of additional stats about your company's Slack usage. However, connecting Slack for Business will not give you access to any actual messages or channels.

Slack - Any Slack account holder can connect Slack. Connecting Slack will not give you access to any messages until you add the Slack app to the channels you care about.