Hashtags are a personal identifier that you use on a post to gain more visibility to a wider audience.They get your content to a larger audience through relevant keywords and phrases specific to your industry and posts. This is why you should use hashtags in every single post on Instagram!
Instagram allows a max of 30 hashtags between your captions and comments, so make sure you are using ALL 30.
Oh, and bigger reach does not mean better results – if you always use hashtags with over 1 million uses, your posts are likely to get lost.