I totally get the comment about not having to think too hard whilst in the process of creating music. Personally, I want to quickly be able to add a sound that's close to what I have in mind, then just get on with the next part of the song. I almost always come back later and tweak, or change, that sound.
I rarely use more than two or so synths per song when writing music; Dimension Pro, Rapture, Z3TA, AD, as well as either True Pianos or Addictive Keys. I try to have a basic working knowledge of the insane amount of presets that are, or I have, installed in these programs. I will find something suitable in a short amount of time so the creative process then has as small an amount of interruption as possible.
I have nothing short of admiration, respect and regard for those musicians that put the time and effort into creating presets for synths and plugs.