Success in Search Engines
Search engine optimization (SEO) starts with valid data coding of HTML and CSS and small data size of your web page. Search engines like google are rating websites better with so called responsive design.
Though your browser shows invalid coded websites, too, search engine spiders take the coding into account and rate good coded sites better.
Another criterium is data size: In DSL times it seemed to be less important whether the images of your domain contain more or less kilo bytes, but for search engines data size is important.
More users search the web via smartphones, therefore search engines like google offer weblinks to websites which work well in situations of bad connectivity, too.
Thousand of sites with too many data make the web slow, even with power servers and thick cables. Google, Yahoo and others do not want to back up this trend, because it minimizes their effectiveness and disposability.
Good handicraft and slim coding help your site beeing located easiliy and ranked higher by search engines.
Accessibility is strengthened by good coding as well - and especially for disabled users surfing the web is important.