Suppose you have downloaded Turbo Delphi and you have created some custom components you wish to use in your application. Borland (or DevCon) states that the Explorer Edition does not allow for custom components to be installed. You need the Professional edition for this, which costs money (under $500, they say).
But what if you have, say a simple component that makes you form transparent and you want to use this in your application. No need for other components to be installed, the rest of the application can do with the standard (200+) components provided. I wouldn't want to pay $500, just to use this single component.
There is more than one possibility to go around this issue. You can of course include the unit in your uses clause and create the component at runtime. This way the component won't be installed in the IDE, but you can still work with it and with its properties.
But there is another way. There is always the DCLUSR Package. You can still install components into this package.
And if you add the component to your form, you even get all the properties and events in the Object Inspector.
Of course, if you want to add lots and lots of components to your installation, and you want to keep them organised in separate packages, you should definately go for the Professional Edition, but if you have just a couple of components to add, or you don't mind the components being all cluttered up in one package, you can use the Explorer Edition.
I don't know if this is breaking the license, but you don't do anything that isn't allowed by the program. I think it is considered hacking and not cracking. I wonder if Borland (DevCo) is going to prevent this method with a new release, or a "hotfix roll-up".