Yep, more important is hitting the sweet spot of the screen with your image size.
You know, I remember seeing the math on how to find that once. In a thread here, I believe. I don't think we're having problems in that area, but I might search for that for the added knowledge.
I like hearing that most of you don't consider the margin a big concern. Zoo's comment about squeegees brings up another couple of questions: How far past the max image width should the squeegee extend? And should the squeegee be shorter than the pallet width, and if so, by how much? Or is overlapping fine? (I tend to think overlapping is asking for press lines & unecessary wear on squeegee, screen, and stencil.) Not asking about what obviously CAN be done, but what's generally GOOD (without going overboard into "in a perfect world" theoretical territory).