Google's John Mueller said it is fine using either root relative links (/google.html) vs relative links (google.html) as long as you are consistent on how you do your URL rewrites, Google can figure it out. Problems can arise when you provide mixed signals to Google and Google gets confused about the direction you are looking to go.
John Mueller said on Twitter "Usually the problems come from sites that do inconsistent URL rewriting (eg "create" subdirectories). If a site has a clean setup, relative links are totally fine."
Here are those tweets:
Both work, if done correctly.
— John ☆.o(≧▽≦)o.☆ (@JohnMu) July 9, 2018
Usually the problems come from sites that do inconsistent URL rewriting (eg "create" subdirectories). If a site has a clean setup, relative links are totally fine. Usually crawlers like @DeepCrawl , @screamingfrog or similar run into the same issues, it's not Google-specific.
— John ☆.o(≧▽≦)o.☆ (@JohnMu) July 9, 2018
John has preached many times of the importance of being consistent - calling it a top SEO piece of advice.
Forum discussion at Twitter.