Frankly I do it all the time especially when trying to whip something up quickly and the end result doesn’t have to look perfect or if all the displays are showing different content and occasional frame drops are acceptable. I’ve always used nVidia Quadro cards and don’t know if this works as well with other GPUs.
However if your displays are all part of a single image and especially if they are next to each other then you risk having issues with performance and/or tearing if you use multiple Window CHOPs. Apparently it also varies according to the GPU used.
So in other words for a potentially large or demanding multi screen project I would try starting with a single Window COMP because it can be painful going back afterwards and having to redo everything because the project was built on “shaky ground”.