Kalamos said:
I must some kind of control freak: when I draw a pic I hate to leave gaps behind.
I want to plan everything out in advance, and it sort of unsettles me when people see something strange or different from what I had initially envisioned.
Alfred Hitchcock (and this may be apocryphal) is quoted as having said that there's nothing more frightening than an unopened door. I believe this is true, so long as there's reason to believe there's something unpleasant on the other side. A person's imagination can fill in all kinds of gaps if you let it, and this is the basic assumption behind leaving room for interpretation in a piece of art.
A more modern example would be Mel Gibson's original intent to release
The Passion of the Christ without subtitles so that the performances would carry the story. He wanted the faces and body language to communicate. I believe that would have worked on a more visceral level, but would have put a significant dent into his ability to make back the money he spent on it.
As for artwork, sometimes I want to make a definitive statement about something, and I try to make it as easily decipherable as possible:
here's what I want you to take away from this experience. In that sense you and I are alike. On the other hand, sometimes I'll want to only
suggest a literary course of action (because illustration
is a form of storytelling) and allow the viewer to fill in the blanks with his/her own fantasies or interpretations. The former method allows the viewer to be entertained without any significant labor, while the latter makes the relationship between artist and viewer more interactive.
It's a question of what you want to accomplish.