depends on how badly you 'rely' on the format. The former usually does what you want with less effort. It may even be better for a special case that you forgot about. An occasional 'long number' may be annoying, but does no real harm if you are calculating the next move in your fantasy football game. In another application, the same behavior could spoil a whole batch of expensive forms (or worse). Clearly the latter is called for. They each have advantages. It is part of a Perl programmer's job to choose appropriately for each application.