@Noman_Ali You heard correct instructions. Personally, we also disable/exclude/stop category, tags even author pages to crawl by any search engine. The only reason is replication, because if we allow Google to crawl our these above pages then duplication will be occur due to content existing on two places, first is post page, second is availability of same content in post category list or tags pages.
Second thing is that, if you disable those pages from crawling then this will not impact on your website traffic. But this one strategy can improve your search engine ranking.