Meta Ads are good at one thing email cannot do: putting your shop in front of people who have never heard of it. Email is good at the thing ads struggle with: getting someone who bought once to buy again without paying for the click a second time.
Run on their own, both leave money behind. Ads without email pay to find a customer, then lose them. Email without ads talks to the same list every month while it slowly shrinks. Together, the ads fill the list and the email turns that list into repeat orders, which makes every pound of ad spend go further.
The longer version, with a simple setup for a small shop, is in Meta Ads and email marketing together.