No Speed button. What's it for?

While creating a proposal on haw to reorganise the Object Buttons, I stumbled across a button I have no idea what is for. The ‘No Speed’ button in the Object Buttons. I know it has to do with Dupliframes, but apart from that I’m lost.

I looked it up in the docs, and here is gives an odd explanation:

No Speed
The “DupliFrames” are set to ‘still’, regardless of the current frame.

This seems rarther odd since objects with Dupliframes always are still and do not move. I’ve tried experimenting with this button on and off in a number of situations, and I have not been able to track down what it does. So, can anyone clear up the confusion?

Thanks in advance.

In general, I think it just means: “Ignore the speed curve”.

For example:

Default scene.
Move it 2 grid spacings to the right, press [.] key, and scale the path about a factor of 4.

Next, parent the cube to the path (Normal Parent)

If you open up an IPO Window (with the path selected) and change the IPO Type in the header to ‘Path’ you will see it’s speed curve.

Now select the Cube, press DupliFrames, and increase ‘Dup Off:’ to about 13, so we can see what happens.

Now compare when ‘No Speed’ is pressed or not:

‘No Speed’ pressed: cube instances are more evenly spaced (ie. the speed curve is ignored)

‘No Speed’ NOT pressed: cube instances are closer together at the start and end of the path due to the “ease in/ease out” shape of the Speed IPO curve.