I request this because it preserves hard edges, meaning there won't be any blending between colors like you get converting with AviSynth, VirtualDub, and of course DGMPGDec currently. This is important for encoders that only work with RGB, where if you transcode video that has been converted using chromaresample="bicubic", the resulting video will have its color edges spreading and bleeding out, while with "point" it won't and will be identical to the source.
I already use the Helix YV12 decoder with progressive video for this purpose, however, I would like to work with interlaced video as well. AviSynth 2.6.0 can convert interlaced with "point", however, it currently shifts the chroma in the process. I've addressed it here
but I'm not sure when it'll get fixed. It would be great to see this properly implemented to DGMPGDec in the meantime.