Confused about cells and Coastlinemaker

Hi all,Quick question, I'm a little confused about Coastline maker and the use of cells and such. I've gotten a picture of a full cell here but that thing must cover a good 30miles by 40 miles or something. Do I really need a whole Cell for a project or can I use the mini cells that show up? Cause at 30 miles by 40 miles you have to make the picture pretty big to get good accurate coast lines.