* Components have a support for customizable UI interfaces for setting the property of components called property sheets and these property sheets are applicable on a component level or at the level of individual property fields in the component. These property sheets show up when you are trying configure a component in the design mode within the IDE. We are not talking about simple text entry type of fields - you can actually do very sophisticated property sheets with tabs, multiple forms etc and what not. It is EXTREMELY configurable and also relatively easy to develop.
* Delphi uses a binary "form" file into which each GUI form persists its interface. So everytime you place a component on a form in the GUI IDE or set its properties, the form and its components have a way of persisting their values into this "form" file. The reverse also happens - so when a form is loaded into the IDE or during runtime, the form fields are read off the "form" file by the form and its components. So the actual .pas file where you are adding code for the events etc is not filled up with a lot of UI related property setting code and so the code looks really clean with clear separation of design and code.
* Components can be installed into the IDE during development very easily
That's not necessarily binary. I don't recall if perhaps it was in Delphi 1 (the 16-bit version for Windows 3.x and Windows 95), but from Delphi 2 or 3 or so (released around the turn of the century), it could also save form definitions as plain text. oh, and of course since the height of the XML craze (shortly after the turn of the century?), in that format too.