Filling out your product descriptions is a valuable activity for your store. It helps both conversions and SEO.
But they can take a looooong time... especially if you have a large catalog or are adding products constantly.
One way to improve this process is to be critical of which products get their descriptions updated first.
Prioritize your best products first. These products are currently selling so a conversion boost on them could be an immediate revenue boost. Since they are your best products, they're also probably watched more closely by Google than the rest of your products.
Then work on the products that could start to become popular in the next 2-3 months. So for example, right now would be too late to get much SEO benefit from Valentines Day products but St. Patrick's Day products are just about right.
This 2-3 month head start gives Google enough time to notice the changes and update the search results.
(From a conversion standpoint, you'll still want to work on your Valentines Day products because better descriptions will help them sell better.)
Don't look for perfection either. It's better to make five products better, than to make one product perfect. You can always come back later and give everything a second update.
Another great optimization for your store is to make sure your product's structured data is setup correctly for Google's Rich Snippets. With those you'll get more traffic and better converting traffic.
You can either audit your store's structured data by hand or install JSON-LD for SEO and have all the structured data you need.
It's already helping over two thousand Shopify stores with their structured data and it could help you too.
Eric Davis