SEO and search engine results
Load speed is a major ranking factor for search engines, if your site loads quickly then it’s more likely to rank higher in search engine result pages.
UX – User Experience and interaction
This ties in with the first reason since users are much more likely to navigate away from your site if it doesn’t load fast enough. If your site does load quickly, then users are more likely to stay on it to read your content or see what you have to offer.
If you should need to hire a professional to optimise your WordPress site for speed then I can recommend this WordPress page speed optimisation service. I’m the project manager over there so you’ll be talking to me.