I used to just do use modulename – then, as my application grew, I found it more and more difficult to find the source to functions (without turning to grep) – some of the other code floating around the office still uses a one-subroutine-per-file, which has its own set of problems, but it makes it much easier to use a text editor to move through the code and quickly track down what you need.
After experiencing this, I’ve become a convert to using use…only whenever possible. I’ve also started picking up Python, and view it the same way as from modulename import *. There’s a lot of great things that modules give you, but I prefer to keep my global namespace tightly controlled.