Nofollow attribute is there to control indexing and serving by search engines. Most search engines will interpret the nofollow link in different ways, affecting the overall site structure and how they understand the information you provide.
rel=Nofollow links has been created to help webmasters to tell Google when NOT to pay attention to external references, documents or web pages related to the information they are sharing and they believe will not help the user or do not endorse. Also, if you are paying for ads with links to your site and that are surrounded by content or other ads that you don’t want to be associated with your website you use nofollow links. Also, if you read this post you will notice that you can tell Google not to crawl specific section of your website that you don’t really need to index such as authorised users only pages where login is required.
The homepage must be accessible or crawlable from everywhere in your website, it is expected. We don’t really know the exact consequences, but you will definitely will have crawling issues and errors will be reported in search engine Console.