In a nutshell
Pains and Gains is a difficult concept as it could be fluffy or blur if not well defined. My inspiration is coming from Value Proposition Canvas and Outcome-Driven Innovation concepts. It is a complement to the Job To Be Done Concept (see Marketing Canvas - Job To Be Done). It measures the outcome of the Job To Be Done: Positive (Gains) when the JTBD is addressed or Negative (Pains) when it is not addressed. So getting to know this is definitely a must for your Marketing Strategy.
In the Marketing Canvas
In the Marketing Canvas, we have identified 6 main categories for building your Marketing Strategy: CUSTOMERS, BRAND, VALUE PROPOSITION, JOURNEY, CONVERSATION and METRICS. Each of these categories, have 4 dimensions which means that a total of 24 dimensions (6 by 4) are defining your Marketing Strategy.
PAINS & GAINS is a one of the 4 dimensions of the CUSTOMERS category.
How to use it?
Pains and Gains help you understanding your customer(s). If you want to build a true customer-centric strategy, you should definitely know whether you understand how your customers evaluate the outcome of their JTBD or not.
It is important to remind you that the Marketing Canvas Method should be applied to one brand and one market (group of customers having same needs and purchase behaviours). You will probably have 2 or 3 personas (having specific JTBD and Pains & Gains). You should thus identify these personas and for each of them, answering the question of Pains & Gains for each persona.
My advise is to start the method with one persona (especially for startup or very small organisation). When you will get used with the method, you can increase the number of personas and complexity the exercise.
Having said that, for each persona, assess whether if you understand how they define/measure/evaluate the positive outcome of the JTBD (Gains) and the negative outcome of not getting the JTBD (Pains).
Is the knowledge of your customers' PAINS & GAINS helping you achieve your goals?
2 answers are possible for this question:
Yes, I really understand the Pains/Gains of my customer: It is an Accelerator because you really know what you could do for helping them to achieve their Job to Be Done
No, I don’t really understand the Pains/Gains of my customer: It is a Brake as you don’t know how to help them achieving their Job To Be Done?
Value Proposition Canvas by Strategyzer, https://www.strategyzer.com/canvas/value-proposition-canvas
Outcome-Driven Innovation, Medium, https://jobs-to-be-done.com/outcome-driven-innovation-odi-is-jobs-to-be-done-theory-in-practice-2944c6ebc40e