1. It shortens your attention span
Picture this. You are waiting for a bus that will come in a few minutes. You're not preoccupied with any thought or activity, what do you do? Probably check your instagram or snap. Shiny, glossy, easily digestible content available at the reach of your fingertips. So what's the problem? The fact that you get used to such easily absorbable entertainment the content that can fulfill you and expand your understanding of this world (e.g. complex articles) becomes more tedious than ever before. Putting little effort into getting your brain stimulated on a daily can take the joy out of thinking thoroughly and analytically in the long run.
2. In some shape or form it is addicting
The likes, the comments, the tags you get on a daily basis get you hooked on the feeling self importance and acknowledgments of your existence. The connections you have with other people increase in quantity and superficiality. Getting used to being constantly acknowledged may force you to feel the obligation to have a prevalent presence online and to keep that dopamine rush you get once a notification pops up. This may not seem harmful but after some time you might find yourself asking friends to take 50 pictures of you for that perfect one, editing pics instead of doing literally anything else and just thinking of the next thing to post to get yourself noticed.
3. Endless comparison
Humans compare, that's what we do, that's how we know our preferences, dislikes, etc. Unfortunately, everything we see online is over hyped, face tuned and filtered through the lenses of lies. Continuously seeing people having fun, traveling and doing other shenanigans inevitably gives you the overall impression that everyone's having a good time all the time. Which can be a downer even if you are having a normal day. We all face the mundane, most of us are on the grind, some of us are sad, but social media is literally for flexing which is an inaccurate representation of people we follow. And if that's all we see to them inevitably have a sense that their life just being as what they show, which can make us self conscious about the quality of life we are living. Or on the contrary, having a fire profile and a lot of attention might give a sense of false superiority and possibly narcissism.
4. Just why?
Social media posting is not for you, it's a reflection of who you want people to see you as, which is silly. The true homies will like you according to your personality and real life conversations, their opinion of you will be completely unrelated to the pictures or videos you post. Also life happens outside of your screens and being so emerged into that world can be almost like stealing from the life you could be living. And if you have an experience you want to share a heartfelt conversation will bring much more fulfillment than an impersonal post with a bunch of likes. So go take some polaroids (tangible pictures are just better), write your friend a letter and look around once in a while. Life doesn't have to be filled with constant stimuli so stop being on your damn phone!