Impressions are the most under-used number in Search Console. Because they are recorded even for results nobody saw, they measure the demand you are eligible for, which makes them the honest base for any traffic forecast — far better than a third-party volume estimate. A page with high impressions and a poor position is an opportunity; a page with no impressions has a relevance or indexing problem, not a CTR problem.
They also explain most confusing CTR reports. An average position of 12 across thousands of long-tail queries produces a CTR that looks terrible next to any published curve, simply because most of those impressions came from the second page.