When do you use StringBuilder.AppendLine/string.Format vs. StringBuilder.AppendFormat?

Question

A recent question came up about using String.Format(). Part of my answer included a suggestion to use StringBuilder.AppendLine(string.Format(...)). Jon Skeet suggested this was

Answer 1

Is it just positively awful to simply use

sbuilder.AppendFormat("{0} line\n", first);

? I mean, I know it's not platform-independent or whatever, but in 9 out of 10 cases it gets the job done.