Usually we import only core modules in `sympy/__init__.py` (for example we don't import physics module by default). There are two main reasons why we may not want to import by default: import speed and global namespace pollution.

bin/test_import gives: 

master: The speed of "import sympy" is: 0.249675 +- 0.005045
crypto: The speed of "import sympy" is: 0.250222 +- 0.006161

(crypto was rebased on top of master) and size of import is:

```
In [1]: import sympy.crypto as c

In [2]: len(filter(lambda x: not x.startswith("__"), dir(c)))
Out[2]: 30
```