I remember, I used to use hash tags on social media to search for pictures or videos of place where I am planning a tour to. ;-) This helped me a lot to have an overview of the place I am going to visit as some people have already visited and posted photos and videos over their. And believe me there's no place where people haven't marked their presence on social media platforms in this materialistic world.
Adding on, people uses hash tags on social media platforms to add their presence via photos or video clips to support an issue, people, organization, song, movie, etc. In such ways, people contribute their love adding their presence which can eventually tell the social media algorithms that this hash tag is popular among people and people love to see related posts and then you will end up seeing similar ads on your browsers, or similar recommended posts or your social media platforms.
Moreover, to search out for a product or an organization people uses hash tags so that they can efficiently search out the desirable destination.
I would say hash tags on social media platforms carry a huge importance and people do often use it to engage audience on their posts too because they know there are many people out their who keeps on searching using hash tags and might end up looking at your post too ;-) , people have got different techniques to build their social life and this is one of it!
I find that the harder I work, the more luck I seem to have.