Using a begin block is preferrable if you can get away with it, but if you can't know whether or not you want to load a module at compile-time, try using 'require' instead of 'use'. 'require' will load the module at run-time. ( 'use' is equivilant to BEGIN { require MODULE; } )

In general, 'use' is preferable because it gives the compiler more information about the symbols in your namespace. For example, where you might have done

use Data::Dumper;
print Dumper $foo;
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You can't just substitute require because then the compiler won't know where the "Dumper" function comes from. Instead you have to do something like

require Data::Dumper;
print Data::Dumper::Dumper($foo);
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