Nobody's required to create an account to post a comment. It's similar to dropping on a WordPress site -- give a name and an optional email address, and you're set. When someone replies to a comment from such an author, that author will be notified via email that someone has replied.
However, there are advantages to creating a dedicated account before commenting:
You'll have quick access to comments you leave across any site.
That's nice from a historical perspective. If you'd like to find a comment you dropped on a blog six months ago, log into your account and dig it up.
You'll be able to delete your comments.
You can't do this if you leave a comment anonymously.
You'll (soon) be given a visual indicator of your realness.
It's not shipped now, but eventually, some sort of UI treat will be left next to comments that were left by authenticated individuals, rather than potentially some internet troll.
JamComments support quickly creating a free account easily on any comment form. Here's how that flow works:
Viewing Past Comments
You can view comments you've left over time by logging in here: