Both.
Good...
- It can help in connecting to other like-minded individuals with similar or same hobbies, interests, beliefs, morals and so on.
- Can be used for self promotion, concerning self-employment/small businesses, talents...stuff like that.
- Can be useful for long distance relationships, such as keeping in touch with family, friends, significant other.
Bad...
-Can encourage those who lack empathy, sympathy, respect, etc to the forefront. Bullying and harassment are issues offline too but how many recognize it or even care to stand up for someone being mistreated whether offline or online?
- Propaganda
- It can help in connecting to other like-minded individuals with similar or same hobbies, interests, beliefs, morals and so on. (Illegal/immoral/etc)
I am sure there are many other reasons others can add to this list of good and bad, but these are the ones that come to mind at the moment.
In essence, it is the person behind the screen that chooses whether they will use social media for the good of society or for the bad of society. Each and every one of us will reap what we sow. If we sow good, in the end we will reap good results and if we sow bad, in the end we will reap bad results.