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

Just create an extension method.

public static StringBuilder AppendLine(this StringBuilder builder, string format, params object[] args)
{
    builder.AppendFormat(format, args).AppendLine();
    return builder;
}

Reasons I prefer this:

• Doesn't suffer as much overhead as AppendLine(string.Format(...)), as stated above.
• Prevents me from forgetting to add the .AppendLine() part at the end (happens frequently enough).
• Is more readable (but that is more of an opinion).

If you don't like it being called 'AppendLine,' you could change it to 'AppendFormattedLine' or whatever you want. I enjoy everything lining up with other calls to 'AppendLine' though:

var builder = new StringBuilder();

builder
    .AppendLine("This is a test.")
    .AppendLine("This is a {0}.", "test");

Just add one of these for each overload you use of the AppendFormat method on StringBuilder.