What is the function of Search Match within Apple Search Ads? What insights doe sit give me and how can they be used?

Apple picks search terms it thinks applies to your app. Saves you from creating keywords, and is a way of maybe discovering keyword combinations you hadn't thought of. Will also tend to match you to search terms used for other apps Apple considers similar to yours.

A very imprecise science, and can be wildly off, but useful for discovery. Recommend creating a specific Search Match only ad group where you bid lower for this than any ad groups where you might be using your own keywords, especially ones where you've carefully crafted the exact match search phrases you want to bid highly for. This way you can more easily separate out the effects of using this.

After time, add negative exact match keywords for any search phrases its using that just don't make sense for your app.