User experience (UX) and search engine optimization (SEO) both depend heavily on website speed. A sluggish user interface/UX site results in bad conversions, low engagement and more bounce rates. By maximizing the performance of your site you provide users on every device a smooth experience.

Improved user experience—pages should load in under two seconds for travel.
Higher SEO Rankings – Google gives first place to quick pages in search results.
Better Conversions: Swifter websites boost sales, registration, and engagement.
Big, uncollapsed images bog down your UI/UX website. apply these methods:
Use software like TinyPNG, ImageOptim, or Squoosh to condense pictures.
Instead of PNG/JPEG, use new formats such WebP.
Lazy load images lets them load only when they are called.
Adjust image dimensions correctly to avoid extra cropping.
Convert SVG icons into inline SVGs will help cut HTTP requests, according to a prolevel advise.
Every page loads several resources: stylesheets, JavaScript, fonts, images. Cutting these requests helps performance go faster.
Merge CSS and JS files into one file if applicable.
For little images/icons, utilize CSS sprites.
Good control over thirdparty software including ad servers, widgets, and tracking tools.
Limit your use of custom fonts to speed up loading times.