For some background on the principles behind the LanX's excellent points,
see Information hiding --
the general idea is to hide your module's implementation (which is likely to change over time) from the (possibly many) programs that call it.
So don't just blindly export all your module's variables!
Instead, think harder about designing a good module interface,
one that will stand the test of time, and so allow you to make many future module improvements
without needing to update in step all your programs that use it.
This topic is discussed in much more detail at: On Interfaces and APIs