It seems to allow modders a whole lot more functionality, and while I've not experimented with it at all myself, I figured I should at least put a link up to it so that people can find it more easily. A PSP ASM tool is so rare and unique it's worth it, I think.
You can find it here.
If anyone has any more to add about this, feel free to mention it in this topic. I know @BleuVII has mentioned using it before, at least, and like I said - there is just no existing discussion about this tool that I can find so far.