Site load speed has become an important part of the website optimization processes. Unlike certain scaling issues, such as site authority or on-page optimization, load speed is probably best viewed as a yes/no factor. Either your site is fast enough or it’s not.
If your site falls into the yes category, then incremental improvements in speed aren’t going to net you much, if any, improvement. However, if your site falls into the no category, you’re likely going to see that negatively impact your exposure in search results–especially via mobile devices.