I like using Spyfu.com for a quick analysis.
Because search engine presence is public, there are tools made to streamline this information about your competitors.
What makes SEO spying useful is that it helps you identify direct competitors and for which keywords.
In a field where every bit of knowledge is useful; you can target competitors and overtake them without them even realizing.
Obviously we can’t take these to be totally accurate. Like with every data tool, it’s important to interperet it with relevance in mind.
It’s really meaningful sometimes to discover new competitors, then you can plan to overtake them. The battle for keywords becomes all out war.