If you're new to Twitter, here's an article for you.
People of all walks of life are on Twitter.
Each with his/her own agenda.
Some use Twitter for business purposes, some to communicate with their friends and loved ones, and some to learn from industry insiders on topics that they find interesting.
Once you have a few tweets under your belt and follow a few hundred people and are followed by a few hundred, the power of Twitter starts to set in.
One of the first things you will notice is that your Twitter timeline featuring the tweets of who you are following will move faster and faster as you add more people to your list.
The problem with this is that it makes the tweets of your followers harder and harder to read as their tweets come from every which way into your timeline.
When you have thousands of followers, your timeline will be moving at the speed of light! To combat this issue, you are left with only one option and that is to unfollow some of your Twitter followers.
It's sad but true.
Even though this is the major reason to unfollow someone, I also thought it would be beneficial to compile a list of some of the other reasons why you might want to unfollow someone besides trying to clean up your Twitter timeline to make it readable.
As you become more familiar with Twitter, you'll understand why I've included these reasons.
In no particular order...

1. Sending you countless direct messages (DMs).
   Often these DMs are requests asking you to "like" a site (more than likely theirs) on the Internet, etc.
   
2. Tweeting a ton of links every day.
   People tend to include links when they tweet.
   When done in moderation it isn't a big deal but when they tweet more than 10 or 20 times a day with links, it can start to get a little aggravating.
   
3. Cross posting tweets from other social media-related sites.
   It's safe to say that many on Twitter are using third party applications to tweet their content that they place on other sites for the sake of convenience.
   Even though it is convenient for the person tweeting, people who are following his/her account will be inundated with post after post from the same source leading to a common theme - aggravation.
   
4. Auto-posting RSS feeds of sites.
   Some set up their Twitter accounts in such a way that they pull the RSS feeds from sites that they like in order to automatically tweet the content in the feeds.
   What this leads to is a mass flood of tweets in the timelines of people who follow you.
   So if you subscribed to the NY Times RSS feed as an example, it would result in having at least 50 tweets be sent out from your Twitter account every single day.
   
5. Retweeting promotions all in uppercase.
   When some people come across a great deal on Twitter, they like to spread the word about it to everyone in their list.
   At times its not frowned upon but when the post is in all UPPERCASE letters trying to draw attention to the promotion and sent multiple times, this normally makes people unfollow others.
   
6. Tweeting past tweets over and over.
   As people don't tend to be monitoring their Twitter accounts 24 hours a day, 7 days a week, some users like to tweet the same content at least once a day or several times a week.
   Although good in theory, people who see the same content repeated over and over will more likely than opt to remove the excessive posting Twitter user from their list of followers.
   

The main takeaway from this post is to be considerate of others so you can minimize the rate of people "unfollowing" you.
On the flip side, if you ever get bombarded with tweets from another user, there's no reason to keep them in your follower list.
Simply click the unfollow button on their account and continue enjoying your Twitter experience.