Your "sweet spot" market is a most defined and narrow group of people / businesses who will benefit from the value you offer.
Example - when I ran a SaaS technology business with a labour cost saving solution developed for the construction market our "Target Market" was the construction market whereas our "sweet spot" market was: -
UK construction companies with an employed workforce (not independent contractors)
350 - 500 employees across multiple sites
Using manual paper based timesheets to track project labour hours
While there were only between 250-350 construction companies in the UK market who qualified based on this criteria, we knew from earlier market research (validation exercise) that this sub-group would: -
A) Benefit the most from the cost savings on offer through use of our solution
B) Result in the fastest sales lead-time
C) Provide us with positive case study examples / referrals within this market sub-group to propel more sales (I will narrow in more on the power of customer studies as a driver of sales growth later in the course).
The ultimate benefit from this narrow market sales approach is hard sales cash hitting your bank account and giving you the life-blood to keep building your business.