Basically Akismet is an awesome comment spam filtering service WordPress websites or blogs. Should you use it? Nothing to lose if you do. Does it cost? There is a free option available for personal and non-business sites. And there are paid options for business websites and blogs.
Here’s a great article about it which explains in detail what it’s all about and how to set it up on your WordPress website: What is Akismet and Why You Should Start Using it Right Away.