From my experience, it can be really powerful, especially using inline assembler to optimize code- a feature that I've not seen so easily used in many IDEs. I have nostalgia for it- from my first real development opportunity being in Delphi 1
I learned programming with Turbo Pascal 6 back in the day, and spent a lot of time with Borland Pascal 7 as well, before moving on. Back then, the Borland IDEs were second to none, the integrated context-sensitive help system was unmatched. And because compilers generally sucked back then, and the machines were slow, the inline assembly feature was pretty good. I moved onto C/C++, but the first couple versions of Delphi were interesting because they made Windows development easy.
But after that? The whole Borland -> Inprise -> Embarcadero mess was reason enough to abandon the language, IMHO. Other, more powerful, languages appeared, several of them without costly licenses. If you want easy GUI, it's hard to beat .NET.
And inline assembly is IMHO useless these days - if there's a substantial speed gain to be had these days, it's usually from writing a large chunk in assembly, enough that you're better off writing it in an external .asm module in a proper assembler. That, or use a language + compiler that has good assembly intrinsics.