Uninstalling an app rarely removes what it put inside your theme. Here is what stays behind and what it costs you.
When you install an app that changes your storefront, it may add code to your theme files. When you uninstall it, Shopify removes the app's access — but the code it wrote can remain exactly where it was.
A script tag pointing at a dead domain still costs a DNS lookup and a connection attempt on every single page view. Browsers wait. Multiply that by a few abandoned apps and you have added real time to your storefront, permanently, for zero benefit. Broken references also produce console errors that make genuine problems harder to find later.
A store that has been running for two years and tried a dozen apps typically has between three and fifteen leftovers. A brand-new store on a fresh theme usually has none, and that is a perfectly good scan result.
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