Twitter is one of the largest social networks out there. Sadly, where you have that much free exchange of dialogue, you also end up with a bunch of people saying and doing some pretty mean and offensive things.
Since bullying, mocking, and other forms of harassment don't always fit in 140 characters, Twitter is now giving users the ability to attach multiple tweets to a single report.
Unlike muting and blocking, reporting is a means of countering abusive behavior, rather than merely tune it out. Twitter says it investigates reports to determine an appropriate response. Attaching multiple tweets gives them more information and provides a better look at the situation. This change doesn't solve the problem, but it gives people one more way to fight back.