Reddit is basically a collection of communities (subreddits) where people discuss specific topics. It can definitely be useful for client hunting, but not in the traditional "cold pitching" way. Most Reddit users dislike direct promotion, so the best approach is to provide helpful answers, share your knowledge, and build credibility over time.
I've seen freelancers and agency owners get clients from Reddit by consistently helping people in relevant subreddits. When someone sees your expertise in your comments and posts, they often check your profile and reach out themselves. Focus on contributing value first, learn the rules of each subreddit, and avoid spamming links. It takes patience, but the leads tend to be more targeted and higher quality than many other platforms.