They're great for continuing lines from side to side. And even side to opposite side.
Works really well when the board has a rounded edge or some wane where the edge is not really sharp and square but the two adjacent faces are square to each other. And the size is perfect and easy to handle and position. Its tons easier to to this job with the saddle square than with a 12" combi square.
https://www.leevalley.com/en-us/shop...saddle-squares
They've gone up in price, I've had mine for years but they are still a bargain compared to Woodpecker's tools. And Veritas tools have always been top notch quality to me. I find I use the bigger one more if you can only get one.
https://youtu.be/EVGkix3nkoA
Helped me lay out these cuts
I have two of them, the first one cost $9.95 IIRC (or $12.95), and I lost it for a while and bought another to replace it at $19.95 I think. Now they are $49.95! The first one that I lost, I was looking for it on the wrong side of the ocean! ;-) (It was here in the States and I was sure I had it with me overseas.) That is my MOST used marking tool.