Honestly, its a mixture of all you said. Some buy them for the sake of buying them and do nothing with the characters afterwards, some buy them and then actually include it in future artwork and stories. Some are lazy, and some see the designs that the artist made and realize how close it was to something they were already working on and decide to go for it and make tweaks afterwards.
I won Crowley through an auction as a cleanslate, only being a visual design, no background info or what. Honestly, I didnt expct to bid on him in the first place but I liked his design too much to pass him up. Luckily for me, I was needing a character of his style for a position in my sona's world and so have a purpose for the big guy.

thanks, it was just something on my mind, and really wanted answered

No problem at all ^^