The Match all feature is designed to boost the match score of all products added to the quiz for questions which are only there for data gathering purposes.
As an example we use a quiz where we ask the question 'How did you hear about us?'. The answer to this question doesn't impact the product recommendations at all, however we still want the products that are already matched in the quiz to gain a match score point regardless of the answer selected here, so for this we enable the Match all toggle:
Please note: Match all is not designed to replace product matching all together. Key products, variants and collections still need to actively be added to the quiz for it to return results.