Well, PyPy does not actually help much with raw number crunching -- a scientist will use numpy for native matrix math, or numba to JIT a tight loop that can't be writted in numpy easily. PyPy really helps in the in-between cases: a few weeks ago I had to write a script to pull a few million rows from a database, process them nontrivially, and dump them to a file. What do I use here? CPython and Ruby will take days. Perl will probably take days, unless I am just doing text processing which perl is optimized for. I can write C or C++, and have the headache of debugging memory errors in a script that will only run once. Or, I can write PyPy and have immensely convenient syntax that will run reasonably quickly (Luajit also occupies this space for me).