A well written meta description can improve CTRS (click-through rates) - i.e. improve the number of people visiting your store from Google.
If you think of a meta description as your first salesman and consider someone searching on Google as a potential customer seeking more information, a good salesman will give enough information to get the customers attention. Similarly, the meta description (along with the page title) is the first thing that your potential customers see about you. The meta description tags should offer enough information to the customer so that he is tempted to visit your store.
The best way to get better at writing good meta descriptions is to actually see what works. I looked at the most successful Shopify stores, to understand how they have written their meta descriptions - and then analyzed them to see what is good, and what could be improved.