Google will pay more attention to your site if it is active. As it has to access your information for ratings.
Keywords will be used more frequently with more content you have on Your Website. With more topics on your site, will come up in more searches.
A website is similar to a car, if you look after a car checking the oil, water, cambelt, tyres it will last longer and efficiently.If something is broken on your car engine it won’t work and will turn of future buyers.
If a website has broken links the user is discouraged and more importantly so is google, as a result affecting your SEO.