Social media can be fun and useful. Your niece in Utah can see your birthday party and you can see her new baby. What's not to like?
The answer of course is not every Facebook or Instagram posting or picture accurately reflects your day to day life or physical condition. Thus, if you've been in a bad crash and are receiving medical care, be aware that any social media posting that includes you in it, can sabotage your case.
You may hurt all the time and be getting physical therapy but if you rally your energy for a picture, that picture may ruin your case later. If your church or social organization performs good deeds be aware that some defense lawyer may mislead a judge or jury in your case down the road, using your peripheral involvement in repairing someone's storm damaged house, to suggest you were wielding a hammer and shovel just fine.
So, what should you do? The answer is be aware of what information is out there on social media concerning you. If you aren't able to work for a period of time because of your injuries, you better make sure there aren't pictures of you doing something else physically demanding during that time period.
Similarly, glorious vacation pictures from Orlando or Hawaii, can convince jurors that you aren't hurt and are trying to get someone else to pay for your vacation.
The bottom-line, use common sense. Let your lawyer know what is being posted so they aren't in for a big, bad surprise later.