how does uniform-stretching work?

[Graham Percival]

Trying to add NEWS items to the docs...

I can't see a difference between these two bars.  If I understand 
uniform-stretching, shouldn't there be a difference?  What's going on 
here?

\paper{ragged-right = ##t}
\score{
<<
  \time 2/4
  \new Staff { c16[ c c c c c c c] c[ c c c c c c c] }
  \new Staff {
          c16[ cisis ces cis c cisis ces cis]
    \override Score.SpacingSpanner #'uniform-stretching = ##t
          c16[ cisis ces cis c cisis ces cis]
  }
>>
}