What does "MLT Processing Threads" affect?

In Settings > Configure Kdenlive > Environment there is a setting for "MLT Processing threads" which is at 1 by default and allows (on my machine) a max value of 3. Now clearly this is about multithreading MLT, but I'm just wondering which parts of Kdenlive this setting would affect?

Playback in the monitor?

It also says >1 is experimental. Does anyone have any idea of *how* experimental it is? Do you have any experience with trying this?

I used the sunab 0.92 release ppa with the 0.8 mlt.
I have the mlt threads on 3. I definitely notice the difference when rendering going from 1 thread to 2 to 3. I have a quad-core i7 which supports 8 threads.
Going higher then 3 doesn't seem to make a big difference so I prefer to keep those threads for other processes.
And the fact that it's experimental: I do quite a lot of (partial) renederings to see the result. I never experienced a quirk in the rendered movie clips (so far).

I don't notice a difference in playback.

I just installed mlt 0.82 by the way. I don't have experience with that version yet.

A long time ago, I tried that at a higher rate but it made the timeline stutter like mad, so I steered clear of it all together. Might be time to experiment again. Cheers.

Using multiple MLT threads is still not flawless. I thought it worked well and it it does work well with "normal" rendering and static titles.
However, I did make this time long horizontal scrolling titles and long vertical scrolling titles. They stutter immensely resulting in a horrible video. Using only one thread for the MLT process resulted in a fluent scroll (but 30% longer rendering times: so be it).