Maybe a silly question ,,, but im gonna sk it anyway casue I dont know the answer

When you buy plug-in software online, and receive only a Product Key via email or whatever, and no CD/DVD hard copy, what happens if you buy a new machine or want to reinstall the program for some reason ??

For eg. I have Nik Software plugins for Aperture that I paid bloody good money for, nearly $400, and only got a product key to activate the program. I am thinking of buying Noise Ninja for Aperture as well.

If I buy another mac, would i just download the trial version again from their site and enter the product key to install and activate it again on the new machine ??

Ive always wondered how this would work if you didnt have a hard copy.