Someone should mention (I guess it is me!) that it is really not recommended to use the lines on the mat, learn to use rulers and the edge of your fabric. Otherwise the mat wears out from cutting on the same lines. Maybe not so badly on the June Tailor but my original Olfa mat tells the tale and because of the deep grooves that formed from me using the mat lines over and over I would have single threads that didn't get cut.
Until you can learn to ignore those pre-printed lines, I think it's better to use the back.
PS: Cutting tip - some fabric is just too close a color to the mat for me to see clearly. A scrap of white paper (or an envelope or whatever is handy tucked under the fabric about half an inch instantly makes it much clearer and more precise as well as faster!