It uses more than 100 MB on my tiny system, I can't really imagine this all just being the configuration of only the chrome browser. How would I reduce its size?
According to the Chromium projects site it's where the users data directory is. So beyond the configuration it will contain the History, bookmarks, cookies, extensions etc.
To minimise the disk usage, you can uninstall extensions you no longer use and get Chrome to clear it's cache/history.
This is the configuration directory of google-chrome. It contains some user data, history, cookies,extensions and bookmarks, crash reports, application cache and safe browsing data...
To know what is consuming your disk storage you can use:
du -h ~/.config/google-chrome
So you can check which directory/file is consuming your disk storage.