When I first started this blog, I had a lot of issues with spam comments. As part of handling that, I made it so that comments from new users had to be approved before appearing. After the first comment was approved, if they used the same credentials, they could post and automatically have the comment appear.
Since then, I have installed some plugins that better handle spam and it catches pretty much all of it now. I feel pretty safe by just allowing comments to appear without approval because it shouldn’t result in 100s of spam comments now. So, until circumstances change, all legitimate comments should automatically appear.