I have wasted so much fabric with crooked cutting! I love my rulers and rotary cutter, but sometimes, as I cut strips and blocks, that darn ruler just twisted a little, and my cut wafted over to the left or right, and I had to waste more fabric cleaning up the edge.
Invisigrip is sold in a piece 12 1/2" by 1 yard long, which was enough for me to do my two most frequently used rulers - my 12 1/2" square, and my 8 1/2" by 24" ruler. Since that initial purchase two years ago, I have bought one more package, which was enough to do most of my smaller templates and rulers. At only $5.99 a package, it is a great investment in saving yourself fabric and frustration. Yay Invisigrip!