If you buy any plugin for personal usage after buying one license you will have 3 keys, but if you change your hardware or reinstall operation system you will need a new key. In 6 months you can ask Support for more keys if you used up all 3.
If you buy the plugin for company usage you need to get a license for each computer (working place), but you are not limited by the keys for it. Just write to support for more keys.