I don't find when useful, except in post mortem situations. The code is the code. Trying to capture history leads to things like old code being commented out to preserve the context. Use a good code repository instead.

git annotate?

I'm talking code that has out-lived several "yeah we'll use this forever" version control systems. If the comment isn't in the code it will get lost.

FWIW you can actually migrate between most major VCS systems without losing your history.

Yes, but it is neigh impossible to migrate from say Python to C, a copy-paste into an entirely different project, and from there via Java to C# and keep history. That may be a stretch, but even one such step will almost certainly lose history.

It also depends on what kind of stuff you've done with your VCS. "Creative" SVN layouts may be difficult to merge.

That's assuming somebody remembers where it was.