Apart from what Rikter stated, I also use DVDDecrypter because it allows you to manually set the layer break in DL DVD's, when Nero does not. One other main reason to use it is because it is freeware (I always have a strong sympathy towards freeware applications). Nero is also a very heavy program with occasional malfunctions, and apart from the fact that it can make compilations, I see no other reason to use it when Alcohol 120% is around. Lastly, Nero sometimes causes a conflict when auto insert notification is disabled in windows XP.
Hence: I HATE Nero.

PS: Someone previously stated that you can burn a working DVD using the compilation option in Nero. True as that may be, it is not suggested, because then the files are not placed on the DVD in the order they should. As a concequence, the Disc will be "less readable" and the seeking time will increase.