There are several reasons to keep your Poser 11. One is the Face Room. Two is Python is different and older scripts won't run correctly if at all. Three the 3D path is also gone. The program itself does not use a lot of space and you can Point 11 to use Poser 12's Library so get rid of duplicated files.

Poser 5, 6, 7, 8, Poser Pro 9 (2012), 10 (2014), 11, 12, 13