What you get
A new domain has no links pointing to it, so search engines have little reason to crawl it. A listing on an established directory gives them a path to your site and a second source that confirms your name, URL and description.
Some directories also send visitors. Launch platforms and AI tool directories have their own audiences who browse for new products, and a listing there can bring your first sign-ups.
What you don't get
Listings don't move you to the top of search results for a competitive keyword. Most directory links are low-value on their own, and several mark their links so that search engines ignore them.
A listing also can't fix a page that doesn't explain the product. If visitors arrive and leave, more listings will bring more visitors who leave.
When to do it
Submit once your landing page says what the product does, who it is for and what it costs. Directory editors reject pages that look unfinished, and a rejected submission is hard to reopen.