If you have package A that looks like:
in reply to Fastcgi and persistence in sub modules
and the script
Then modules A, B, and C will be loaded during script compilation time. Even if you place use A inside the while loop or after it (see use). If it is a good practice or not depends on your particular conditions. If you have pre-forking server running on some sort of Unix it is advisable to preload modules as it will reduce total memory usage due to COW.