vc-find-revision-no-save?

[John Yates]

(I am working on incorporating git-timemachine-like functionality into
vc.  If I should post questions such as the following in
help-gnu-emacs, just let me know.)

vc.el contains the following defcustom:

    (defcustom vc-find-revision-no-save nil
      "If non-nil, `vc-find-revision' doesn't write
the created buffer to file."
      :type 'boolean
      :version "27.1")

Notice that the default is nil.  What is the logic in allowing an
historic revision to be associated with a file?  Why is it not merely
a readonly buffer with no backing file?

Perhaps I have been too influenced by git...  My mental model is that
revisions are immutable _values_.  Is that not vc's model?