Polarization in the United States is not necessarily a bad thing. There are consequences, of course, and some of which are bad and some of which are good. I found a few websites you can check out that have some simple explanations of some of the consequences associated with polarization and I will post them below.
In brief, there are two major political parties in the United States - Democrats and Republicans. These two parties are becoming increasingly more separated than they have been in previous decades. This separation gives voters more realistic options when they are choosing who to vote for.
However, as political parties shift towards extremes and people gradually mistrust the members of the other political group, it has become difficult for politicians to agree on a path forward. Congress is more likely to freeze and find it difficult to pass legislation, while elections and partisan media can become more divisive.
You can imagine some of the consequences of Congress not being able to agree, right?
Look at these pages for more information, if you need it.
I hope I helped!