Yes I understand that it is cooler to design your own sounds, but I think there are 2 creative modes in synth music creation. One is triggered by a new sound design, the other is triggered by a chord progression or melody inspiration. In the latter, I feel the need to be able to switch on a "standard" sound quickly (string, brass, piano, electrical piano, harp, organ, distorted guitar, etc.) to elaborate on it before it is too late and gone from my memory forever.
I am now busy building that bank of sounds.