Well in the context of kvnwpts post
"3 days ago I started to follow everyone to gain followers, and in 3 days I've been followed by 950 people wich means I can reach 10k followers pretty easy"
If he is following people for the sole purpose of gaining followers then it is smart to un follow anyone that does not follow you back. However, I have learned from several years on twitter that its not about building as many followers as possible its about connecting with people and having something to say that people are interested in hearing.
If you can accomplish that then twitter can be a useful tool for your business. If you just build a huge following of people and don't interact with anyone or provide useful content then they will just ignore you.