Add note on minimising unused code

This feels like an omission – minimising any unused code should be a 'high priority' task when it comes to web performance

source/standards/optimise-frontend-perf.html.md.erb

@@ -20,11 +20,12 @@ For example:
 | #High    | Position assets correctly                                                        | [Set styles at the top of the page][] and [`defer` scripts][].                                                                                                                                                                                                 |
 |          | Compress static resources                                                        | [Minify][] CSS and JavaScript and use a compression algorithm like [Gzip][] and [Brotli][] on assets.                                                                                                                                                          |
 |          | Set correct Headers                                                              | Set correct [Cache-Control][] and [ETag][] headers on assets for optimal caching.                                                                                                                                                                              |
+|          | Minimise unused code                                                             | Avoid including CSS and JavaScript that is not used on your site.                                                                                                                                                                                              |
 | #Medium  | Include `width` and `height` attributes on images to minimise layout thrashing   | Make sure to include these attributes to improve visual stability and the [Cumulative Layout Shift (CLS)][] metric.                                                                                                                                            |
 |          | Minimise TCP connections                                                         | Use fewer third-party domains to reduce the number of DNS + TCP + SSL negotiations per page.                                                                                                                                                                   |
 |          | Investigate [lazy loading][]                                                     | For pages with many images, only load images in the immediate browser viewport.                                                                                                                                                                                |
 |          | Investigate the impact of loading [@font-face][] assets on perceived performance | Use the CSS `font-display` property or other [font-loading strategies][] to manage common issues like [FOUT, FOIT and FOFT][].                                                                                                                                 |
-|          | Minimise HTTP requests                                                           | Minimise the number of CSS and JavaScript files to reduce the number of round-trips to the server. See ‘Code splitting’ below.                                                                                                                                                   |
+|          | Minimise HTTP requests                                                           | Minimise the number of CSS and JavaScript files to reduce the number of round-trips to the server. See ‘Code splitting’ below.                                                                                                                                 |
 | #Low     | Reduce cookie size                                                               | Because every cookie is sent with each HTTP request, enable HTTP/2 to enable HPACK header compression or HTTP/3 for QPACK.                                                                                                                                     |
 |          | Investigate using a Content Delivery Network (CDN)                               | A CDN will improve site performance by using a network of servers to deliver resources to users. The user will get delivered resources from the server that is located nearest to the user. A CDN is well-suited to handling heavy traffic and traffic spikes. |
 |          | Keep JSON payloads small                                                         | Avoid adding too much data to JSON objects, as parsing them can be slow.                                                                                                                                                                                       |