With Shopify you can't run anything locally, it's all in their cloud. So you're constantly typing CSS into a textbox in a web site. Also pretty much every Shopify plugin ("app") costs $5 or $10 per month which adds up fast. Wordpress plugins are pretty money hungry too but it's much worse on Shopify.
It's ok if you're just making small tweaks to a theme that is already 80% of what you need.