A SEO expert may use one or several SEO tools to deliver the SEO service. When improving the SEO for a website, yours or his own, that expert need to count the website loading time and he won't probably start counting the second or minutes until the website it's loading each time when he's making a change and it's testing it. He has tools for doing that. He also need to analyze the structure and he can do it himself but the online SEO tools can analize the website page or blog post faster than he can do it.
You can do the SEO yourself or you can hire somebody (a person or a company) for doing that. Either way, you should know there are some online SEO tools for everyone who wants to do that.