This would be very useful.
This would make one face of the prim always point towards all viewers making it like a 2-dimensional object.
Huds are similar but they only work for the wearer.
You can achieve something similar using a long lasting particle, but a prim is much more versitile than a particle as for example you could use animations and all the texture options like repeats per face, offset, shinyness, bumpmaps etc.