What you need to know
Large client bundles take time to download, parse, and execute, especially on lower-end phones. A small dependency or an oversized client boundary can have a larger effect than a tiny CSS change.
How to apply it
Inspect bundle analysis, replace heavy packages when a native API works, split rarely used routes, and keep static page content on the server. Measure the real route after each change.
Common mistake to avoid
Do not remove a useful feature just to chase a bundle number. Focus on code users download but do not need for their current task.