I'm left to guess at what you mean by this exactly, but, .gitignore only helps with things that are agreed to be ignored by everyone. Files that are more specific to a particular developer or workflow don't always fit in there well.

But, I'm not sure that's what this new capability helps with anyway.

So, please elaborate.

part of the --untracked-cache feature is to reduce the cost of applying .gitignore patterns. When you have tons of files to check against some patterns, even strcmp() accumulates up.