Quote Originally Posted by Ken Lee View Post
What is the benefit of a mildly acid stop bath ? Is it to arrest development more instantaneously and completely ?
It does that, though film usually goes through the water bath and into the fixer rapidly enough that it doesn't matter.

As per Sandy's experience, the stop bath protects the fixer from the alkalinity of the developer. It's more important in printing, as paper developers are much stronger, more work passes through the solutions, and if you're using fiber-based paper, more developer follows a given sized piece of paper as it's absorbed into the paper.

I use a stop bath in printing, but not with film, just a quick dip in the water there...