Depending on the size of the project determines if I use the mat grids or the grids on the ruler. It is a personal preference. I don't like being told I am doing something wrong, when it comes out right the way I do it. Each one of us are unique in out styles and the way we do things. What works for me as a right handed person may not work for someone else who is also right handed. Next time ask for their badge. If they don't have a badge, tell them with no dis-respect I will do it my way!!!!! Do whats comfortable to you, and enjoy your craft.